JP6975559B2 - Squint objective optical system and a squint endoscope equipped with it - Google Patents

Description

The present invention relates to a squint objective optical system provided with an optical path conversion element and a squint endoscope provided with the same.

In recent years, in image pickup devices such as CCD (Charge Coupled Devices) and C-MOS (Complementary Metal Oxide Semiconductor), the miniaturization of pixels and the miniaturization of the device itself are progressing due to the progress of miniaturization technology. Particularly recently, an image pickup device having very fine pixels, for example, an image pickup device having a pixel pitch of about 1 to 2 μm has been manufactured. As described above, the image sensor in recent years has become smaller with more pixels than before.

Further, if the outer diameter and the total length of the lens of the objective optical system are reduced, it becomes difficult to make the light rays emitted from the objective optical system vertically incident on the light receiving surface of the image pickup device. In this case, the light beam is obliquely incident on the light receiving surface (hereinafter referred to as oblique incident). For this reason, recent image pickup devices such as CCDs and C-MOSs are designed on the premise that the optimum light beam incident on the light receiving surface is oblique incidence. As described above, recent image pickup devices have oblique incident characteristics.

By using a multi-pixel, small image sensor for the endoscope, it is possible to improve the image quality and reduce the diameter of the endoscope. Along with this, a high-performance and compact objective optical system is required for the objective optical system for endoscopes. The high-performance optical system is, for example, an optical system having high resolution and well-corrected aberration.

When the pixel pitch becomes as small as about 1 μm, when the F number of the optical system is large, the optical performance is deteriorated due to the influence of diffraction. Therefore, the optical system used for the image sensor having a small pixel pitch must be an optical system having a small F number. However, as the F number becomes smaller, the diameter of the light flux passing through the optical system becomes larger. Therefore, if the F number is reduced, it becomes difficult to perform aberration correction satisfactorily.

In the optical system used for an image pickup device having a small pixel pitch, each aberration must be corrected so that the amount of each aberration generated becomes very small in accordance with the narrowing of the pixel pitch. For example, in terms of the amount of lateral aberration, the amount of aberration must be set to a level several times the pixel pitch, that is, about several μm, or at most 10 μm or less.

If an attempt is made to satisfactorily correct the aberration of the optical system to such a level, the number of lenses in the optical system will increase. However, if the number of lenses is increased too much, the total length of the optical system becomes long. Further, as the overall length of the optical system becomes longer, the height of the light rays passing through the lens also becomes higher, so that the outer diameter of the lens also becomes larger. Endoscopes require a small optical system. Therefore, it is necessary to configure the objective optical system so that the size applicable to the endoscope and high imaging performance are secured while suppressing the increase in the number of lenses as much as possible.

Further, one of the objective optical systems for endoscopes is a perspective objective optical system. In the perspective objective optical system, anterior vision, lateral vision, or posterior vision is performed.

FIG. 1 is an example of a conventional perspective objective optical system. The perspective objective optical system 1 is a perspective objective optical system for lateral viewing. The perspective objective optical system 1 is composed of a front lens group 2, a prism 3, and a rear lens group 4. In the perspective objective optical system 1, the optical axis of the front lens group 2 and the optical axis of the rear lens group 4 are orthogonal to each other by the prism 3.

FIG. 2 is another example of the conventional perspective objective optical system. The perspective objective optical system 5 is a perspective objective optical system that performs forward viewing. The perspective objective optical system 5 is composed of a front lens group 6, a prism 7, and a rear lens group 8. In the perspective objective optical system 5, the optical axis of the front lens group 6 and the optical axis of the rear lens group 8 are crossed by the prism 7. However, the two optical axes are not in an orthogonal state.

As shown in FIGS. 1 and 2, in the perspective objective optical system, an optical path conversion element having a large glass path length is arranged in the optical system. Therefore, especially in the perspective objective optical system, a large space for arranging an optical path conversion element, for example, a prism is required. As a result, the total length of the perspective objective optical system is longer than that of the direct-view objective optical system. As described above, since the perspective objective optical system tends to be larger than the direct view objective optical system, the perspective objective optical system is required to be further miniaturized.

Patent Documents 1 to 6 disclose perspective objective optical systems.

The perspective objective optical system disclosed in Patent Document 1 is composed of a front group divergent lens system and a rear group convergent lens system. This perspective objective optical system is an optical system that is premised on being used for an image fiber. Therefore, in these objective optical systems, the light rays emitted from the objective optical system can be incident substantially perpendicular to the incident end face of the fiber.

The perspective objective optical system disclosed in Patent Document 2 is composed of a first lens group composed of one negative lens and a second lens group having a positive refractive power. In this perspective objective optical system, a glass material having a small dispersion (a glass material having a large Abbe number) is used for the negative lens and the prism of the first lens group for chromatic aberration correction.

The perspective objective optical system disclosed in Patent Document 3 is composed of a front group having a negative focal length and a rear group having a positive focal length.

The perspective objective optical system disclosed in Patent Document 4 includes a first lens group composed of a single lens having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. And, it is composed of.

In this perspective objective optical system, the third lens group is composed of a junction lens composed of a negative lens and a positive lens in order from the object side. By doing so, telecentricity is ensured. That is, in the perspective objective optical system disclosed in Patent Document 4, the light rays emitted from the perspective objective optical system can be incident substantially perpendicular to the light receiving surface of the image pickup element.

The perspective objective optical system disclosed in Patent Document 5 is composed of a negative first group and a positive second group.

The perspective objective optical system disclosed in Patent Document 6 is composed of a front lens group composed of a negative lens, an optical path conversion element, a brightness aperture, and a rear lens group having a positive refractive power. The rear lens group consists of a positive lens and a junction lens having a positive refractive power.

Japanese Unexamined Patent Publication No. 51-62053 Japanese Patent No. 3385090 Japanese Patent No. 3574484 Japanese Patent No. 4439184 Japanese Patent No. 4814746 Japanese Patent No. 6001227

In the perspective objective optical system disclosed in Patent Document 1, the entire optical system is large and the optical performance is insufficient.

Therefore, the perspective objective optical system and the direct view objective optical system disclosed in Patent Document 1 can be applied to an image pickup element such as a CCD having a large number of pixels and small size, that is, for high performance and miniaturization. It cannot be applied to the corresponding perspective objective optical system.

In the perspective objective optical system disclosed in Patent Document 2, a glass material having a low refractive index is used for each of the negative lens and the prism of the first lens group for chromatic aberration correction. In this case, in particular, the air conversion length on the object side is longer than that of the brightness diaphragm. As a result, the outer diameter of the negative lens and the outer diameter of the prism become large. Further, since the F number is also large, the optical performance is insufficient for use in an image pickup device having a small pixel pitch.

Therefore, the perspective objective optical system disclosed in Patent Document 2 cannot be applied to a perspective objective optical system corresponding to high performance and miniaturization.

In the perspective objective optical system disclosed in Patent Document 3, the entire optical system is large because the back focus is long.

Further, since the focal length of the negative lens in the front group is small, the negative refractive power of the front group is large. On the other hand, in the rear group, the focal length of the junction lens is long in order to secure a long back focus. Therefore, the positive refractive power of the rear group is small. In the case of an optical system composed of two lens groups, if the balance between the negative refractive power and the positive refractive power is lost, various aberrations are greatly generated. As described above, in the perspective objective optical system disclosed in Patent Document 3, the optical performance is not sufficient because the balance of the refractive power in the entire optical system is poor.

Therefore, the perspective objective optical system disclosed in Patent Document 3 cannot be applied to a perspective objective optical system corresponding to high performance and miniaturization.

The perspective objective optical system disclosed in Patent Document 4 ensures telecentricity. However, since recent image pickup devices have oblique incident characteristics, it is not necessary to ensure telecentricity in the optical system. In the perspective objective optical system disclosed in Patent Document 4, the angle of the light beam emitted from the perspective objective optical system is rather deviated from the angle that satisfies the oblique incident characteristic of the image pickup element. As a result, uneven brightness and uneven color occur in the peripheral portion of the image.

Therefore, the perspective objective optical system disclosed in Patent Document 4 cannot be applied to a perspective objective optical system corresponding to high performance and miniaturization.

In the perspective objective optical system disclosed in Patent Document 5, the overall length of the optical system and the back focus are long in order to arrange the filters. Therefore, the entire optical system is large.

Further, since the angle of view is large, the focal length of the first group is small (the negative refractive power of the first group is large). On the other hand, as described above, since the total length and back focus of the optical system are long, the focal length of the second group is long (the positive refractive power of the second group is small). In the case of an optical system composed of two lens groups, if the balance between the negative refractive power and the positive refractive power is lost, curvature of field and astigmatism occur. Further, in the perspective objective optical system disclosed in Patent Document 5, since the image height is high, the outer diameter of the lens of the second group is also large.

Therefore, the perspective objective optical system disclosed in Patent Document 5 cannot be applied to a perspective objective optical system corresponding to high performance and miniaturization.

The perspective objective optical system disclosed in Patent Document 6 is an optical system having an F number of about 3.6. In the perspective objective optical system of each embodiment disclosed in Patent Document 6, since the F number is large as a whole, it is easily affected by diffraction due to the miniaturization of the pixels of the image pickup device. Therefore, it is difficult to use the perspective objective optical system disclosed in Patent Document 6 together with an image pickup device having a small pixel pitch.

Further, as the image sensor becomes smaller, the image height of the objective optical system also becomes smaller. In the perspective objective optical system disclosed in Patent Document 6, the angle of view of the optical system becomes smaller as the image height becomes smaller. Further, in the case of an endoscope, there is a desire to observe a wider range, but the perspective objective optical system disclosed in Patent Document 6 cannot widen the observation range.

Therefore, the perspective objective optical system disclosed in Patent Document 6 cannot be applied to a perspective objective optical system corresponding to high performance and miniaturization.

As described above, it is difficult to realize a perspective objective optical system corresponding to high performance and miniaturization with the objective optical system disclosed in Patent Documents 1 to 6.

The present invention has been made in view of such problems, and an object of the present invention is to provide a high-performance and compact perspective objective optical system. In addition, a high-quality image can be obtained, and a perspective endoscope having a reduced diameter tip portion is provided.

In order to solve the above-mentioned problems and achieve the object, the perspective objective optical system of the present invention is used.
From the object side, it consists of a front lens group having a negative refractive power, an optical path conversion element, a brightness aperture, and a posterior lens group having a positive refractive power.
The front lens group consists of front negative lenses.
The rear lens group consists of a rear positive lens and a junction lens having a positive refractive power.
It is characterized by satisfying the following conditional expressions (1) and ( 3').
4.0 <f2 / f <12.0 (1)
2.652 ≤ fR / f <3.8 (3')
here,
f2 is the focal length of the rear positive lens,
f is the focal length of the entire perspective objective optical system,
fR is the focal length of the rear lens group,
Is.

Further, the perspective endoscope of the present invention is characterized by including the above-mentioned perspective objective optical system.

According to the present invention, it is possible to realize a high-performance and compact perspective objective optical system. In addition, a high-quality image can be obtained, and a perspective endoscope having a reduced diameter tip can be provided.

It is a figure which shows the conventional perspective objective optical system. It is a figure which shows another conventional perspective objective optical system. It is a figure which shows the cross-sectional structure of the perspective objective optical system of this embodiment. It is a figure which shows a prism. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 1. FIG. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 2. FIG. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 3. FIG. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 4. FIG. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 5. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 6. It is a figure which shows the cross-sectional structure of the perspective objective optical system which concerns on Example 7, and is an aberration diagram. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 8. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 9. FIG. It is a figure which shows the cross-sectional structure of the perspective objective optical system which concerns on Example 10, and is an aberration diagram. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 11. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 12. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 13. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 14. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 15. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 16. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 17. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 18. It is a figure and the aberration diagram which show the cross-sectional structure of the perspective objective optical system which concerns on Example 19. It is a figure which shows the structure of an endoscope apparatus.

Hereinafter, the reason and operation of the perspective objective optical system and the perspective endoscope provided with the perspective objective optical system according to the present embodiment will be described with reference to the drawings. The present invention is not limited to the perspective objective optical system according to the following embodiment and the perspective endoscope provided with the perspective objective optical system.

The perspective objective optical system of the present embodiment comprises a front lens group having a negative refractive power, an optical path conversion element, a brightness aperture, and a rear lens group having a positive refractive power in order from the object side. The front lens group is composed of a front negative lens, and the rear lens group is composed of a rear positive lens and a junction lens having a positive refractive power.

By arranging the optical path conversion element in the vicinity of the brightness diaphragm, that is, on the object side of the brightness diaphragm or the image side of the brightness diaphragm, the light beam height in the optical path conversion element can be suppressed low. As a result, the size of the optical path conversion element can be reduced.

However, if the optical path conversion element is arranged on the image side of the brightness diaphragm, the distance from the brightness diaphragm to the image plane becomes at least longer than the glass path length of the optical path conversion element. Then, the light beam emitted from the perspective objective optical system becomes substantially perpendicular to the light receiving surface of the image sensor. Therefore, the angle of the light beam emitted from the perspective objective optical system does not satisfy the oblique incident characteristic of the image pickup device. As a result, uneven brightness and uneven color occur in the peripheral portion of the image.

In addition, when assembling the perspective objective optical system, focus adjustment is performed. Therefore, if the oblique incident characteristics of the image sensor are forcibly satisfied, the interval required for focus adjustment is insufficient. In addition, since the light beam is forcibly bent according to the oblique incident characteristic, aberration occurs. As a result, the optical performance is significantly reduced.

Therefore, in the perspective objective optical system according to the present embodiment, the optical path conversion element is arranged on the object side of the brightness diaphragm. As a result, the distance from the brightness diaphragm to the image plane can be shortened, so that the angle of the light beam emitted from the perspective objective optical system can be relatively easily set to an angle that satisfies the oblique incident characteristics of the image pickup element.

Further, by arranging the optical path conversion element on the object side of the brightness diaphragm, the niter path length becomes longer on the object side than the brightness diaphragm. Therefore, the length of the frame member that holds the front lens group can be appropriately secured. As a result, the perspective objective optical system can be assembled and the perspective objective optical system can be easily attached to the tip of the endoscope with high accuracy.

In addition, it is necessary to widen the optical system for wide-range observation. When the angle is widened, the refractive power of the negative lens located closest to the object is mainly increased. This negative lens is composed of a plano-concave lens having a concave surface facing the image side and a meniscus lens having a concave surface facing the image side.

When the refractive power of this negative lens becomes large, the radius of curvature of the image side surface of the plano-concave lens and the radius of curvature of the image side surface of the meniscus lens become small. If this radius of curvature becomes too small, the workability of the lens deteriorates.

Further, the plano-concave lens and the meniscus lens are held by the objective frame. In this case, eccentricity due to processing error and eccentricity due to assembly error occur between the objective frame and the lens. When the refractive power of the lens becomes large, the optical performance is significantly deteriorated due to the eccentricity of the lens.

In order to reduce the deterioration of optical performance due to the eccentricity of the lens, the processing accuracy of the lens and the processing accuracy of the objective frame may be made stricter than ever. However, increasing the processing accuracy to suppress the amount of eccentricity of the lens significantly deteriorates the processability of the parts, and if the processing accuracy is increased and the outer diameter clearance between the lens and the frame disappears, it is difficult for the lens to enter the frame. Assembling workability also deteriorates.

In particular, when the pixel pitch of the image sensor becomes small, the deterioration of the optical performance due to the eccentricity of the lens becomes remarkable. Therefore, it is necessary to configure the optical system so that the influence of the eccentricity of the lens on the optical performance is reduced.

Also in the perspective objective optical system of the present embodiment, the front negative lens is arranged on the object side in order to widen the angle of the optical system. However, an optical path conversion element is arranged between the front negative lens and the brightness diaphragm. Therefore, the distance between the front negative lens and the brightness diaphragm can be widened.

If the distance between the front negative lens and the brightness diaphragm is widened and the two are separated from each other, the height of the light beam in the front negative lens increases, so that the diameter of the front negative lens becomes slightly larger. However, by separating the two, it is possible to suppress an increase in the refractive power of the front negative lens. As described above, in the perspective objective optical system of the present embodiment, the increase in the refractive power of the front negative lens is suppressed, so that the deterioration of the optical performance due to the eccentricity of the lens can be reduced.

It is desirable that the junction lens is composed of a positive lens and a negative lens in order from the object side. By doing so, the perspective objective optical system can be miniaturized. Further, the angle of the light beam emitted from the perspective objective optical system can be set to an angle that satisfies the oblique incident characteristics of the image pickup device.

If the junction lens is composed of a negative lens and a positive lens in order from the object side, the height of the light beam in the junction lens becomes high, so that the outer diameter of the lens becomes large. Therefore, the processability of the lens deteriorates. In addition, the outer diameter of the entire perspective objective optical system becomes large.

Further, since the light rays are bent by the action of the positive lens arranged on the image side, the light rays emitted from the perspective objective optical system are substantially perpendicular to the light receiving surface of the image pickup device. As a result, it becomes difficult to set the angle of the light beam emitted from the perspective objective optical system to an angle that satisfies the oblique incident characteristics of the image pickup device. If the angle is forcibly satisfied with the oblique incident characteristic, the light beam is greatly bent at the junction lens surface, and aberration occurs. Therefore, the optical performance is deteriorated.

The perspective objective optical system of this embodiment satisfies the following conditional expression (1).
4.0 <f2 / f <12.0 (1)
here,
f2 is the focal length of the rear positive lens,
f is the focal length of the entire perspective objective optical system,
Is.

The conditional expression (1) is a conditional expression that defines the focal length of the rear positive lens.

If it falls below the lower limit of the conditional expression (1), the focal length of the rear positive lens becomes too small. In this case, the image position is too close to the rear lens group, so that the interval required for focus adjustment is lost.

In addition, the oblique incident angle of the light beam on the image plane becomes too large. Therefore, the angle of the light beam emitted from the perspective objective optical system cannot be set to an angle that satisfies the oblique incident characteristics of the image pickup device.

In addition, since the refractive power of the rear positive lens becomes too large, the light beam is greatly bent by the rear positive lens. In this case, the spherical aberration becomes excessively corrected, and the coma aberration also becomes large. Therefore, the optical performance is deteriorated.

If the upper limit of the conditional expression (1) is exceeded, the focal length of the rear positive lens becomes too large. In this case, since the image position is separated from the rear lens group, the interval required for focus adjustment can be secured. However, since the adjustment interval becomes too large, the total length of the optical system becomes long. Therefore, the optical system becomes large.

In addition, the angle of oblique incidence on the image plane becomes too small. Therefore, the angle of the light beam emitted from the perspective objective optical system cannot be set to an angle that satisfies the oblique incident characteristics of the image pickup device.

Further, since the refractive power of the rear positive lens becomes too small, the light beam cannot be bent so much by the rear positive lens. In this case, the spherical aberration becomes insufficiently corrected, and the coma aberration also becomes large. Therefore, the optical performance is deteriorated.

The perspective objective optical system of the present embodiment preferably satisfies the following conditional expression (2).
0.4 <f3 / f2 <1.5 (2)
here,
f2 is the focal length of the rear positive lens,
f3 is the focal length of the junction lens,
Is.

The conditional expression (2) is a conditional expression that defines the focal length of the rear positive lens and the focal length of the junction lens.

By satisfying the conditional expression (2), the balance between the refractive power of the rear positive lens and the refractive power of the junction lens can be optimized.

If it is less than the lower limit of the conditional expression (2), the focal length of the junction lens becomes too small with respect to the rear positive lens, so that the positive refractive power in the rear lens group becomes too large. In this case, the image position gets too close to the rear lens group, so that the interval required for focus adjustment becomes narrow. That is, the interval required for focus adjustment is insufficient. Further, the angle of view becomes large and the front lens group becomes large.

Further, regarding the focusing range on the object side, a preferable range and a preferable position with respect to the optical system (a preferable near point position or a preferable far point position) are predetermined depending on the application of the perspective objective optical system. There is. In reality, a range slightly wider than the preferable range is secured as the focusing range. By doing so, it is possible to have some margin in the actually secured focusing range with respect to the preferable range.

Since it is necessary to reduce the F number of the optical system used for the image pickup device having a small pixel pitch, the preferable range is narrower than that of the conventional optical system. In this case as well, the preferable range can be covered by making the actually secured focusing range slightly wider than the preferable range. However, in an optical system having a small F-number, even in this way, it is difficult to obtain a sufficient margin for a preferable range in the actually secured focusing range.

Therefore, if the position of the near point of the actually secured focusing range is slightly closer to the optical system than the preferable position, the range on the far point side becomes insufficient, and the object located at the far point is focused. It becomes impossible to observe in the apogee state. Also, if the position of the far point in the actually secured focusing range is slightly farther from the optical system than the preferable position, the range on the near point side will be insufficient, and the object located at the near point will be focused. It becomes impossible to observe in the state of matching.

Further, it is not possible to increase the F number of the optical system in order to widen the focusing range because the image quality is deteriorated due to the influence of diffraction of the optical system. Further, reducing the focal length of the optical system in order to widen the focusing range increases the angle of view of the optical system and causes an increase in the size of the front lens group.

When the value is below the lower limit of the conditional expression (2), the position of the in-focus range actually secured is farther from the perspective objective optical system than the preferable position. In this case, the position of the near point in the actually secured focusing range is farther from the perspective objective optical system than the position of the preferable near point. Therefore, it becomes difficult to form an image of an object located at a preferable perigee in an in-focus state.

Further, coma aberration is greatly generated in the negative direction in the peripheral portion of the image. Therefore, the optical performance is deteriorated.

Further, for example, when the junction lens has a positive lens and a negative lens, the balance between the refractive power of the entire positive lens and the refractive power of the entire negative lens in the rear lens group is lost. As a result, axial chromatic aberration and chromatic aberration of magnification occur. Therefore, the optical performance is deteriorated. When used with an image sensor with a small pixel pitch, the effect on the deterioration of optical performance is significant.

Also, the focal length of the junction lens becomes too small. That is, the refractive power of the junction lens becomes too large. In this case, since the radius of curvature of the lens surface becomes small, it becomes difficult to process the lens constituting the junction lens. When the junction lens has a positive lens and a negative lens, both the positive lens processing and the negative lens processing become difficult.

If the upper limit of the conditional expression (2) is exceeded, the focal length of the junction lens becomes too long, so that the positive refractive power in the rear lens group becomes too small. In this case, the image position is too far from the rear lens group, so that the length of the glass path from the brightness diaphragm to the image position becomes long. As a result, the total length of the optical system becomes long. In addition, the entire optical system becomes large.

Further, since the angle of view becomes small, the observation range of the optical system becomes narrow. Further, since the focal length of the entire perspective objective optical system becomes large, the focusing range becomes narrow.

Further, the position of the in-focus range actually secured is closer to the perspective objective optical system than the preferable position. In this case, the position of the far point in the actually secured focusing range is closer to the perspective objective optical system than the position of the preferable far point. Therefore, it becomes difficult to form an image of an object located at a preferable apogee in an in-focus state.

In addition, coma aberration is greatly generated in the positive direction in the peripheral portion of the image. Therefore, the optical performance is deteriorated.

Further, for example, when the junction lens has a positive lens and a negative lens, the balance between the refractive power of the entire positive lens and the refractive power of the entire negative lens in the rear lens group is lost. As a result, axial chromatic aberration and chromatic aberration of magnification occur. Therefore, the optical performance is deteriorated. When used with an image sensor with a small pixel pitch, the effect on the deterioration of optical performance is significant.

Also, the focal length of the rear positive lens becomes too small. That is, the refractive power of the rear positive lens becomes too large. In this case, since the radius of curvature of the lens surface becomes small, it becomes difficult to process the rear positive lens.

The perspective objective optical system of the present embodiment preferably satisfies the following conditional expression (3).
2.3 <fR / f <3.8 (3)
here,
fR is the focal length of the rear lens group,
f is the focal length of the entire perspective objective optical system,
Is.

The conditional expression (3) is a conditional expression that defines the focal length of the rear lens group.

Below the lower limit of the conditional expression (3), the positive refractive power in the rear lens group becomes too large. In this case, the image position gets too close to the rear lens group, so that the interval required for focus adjustment becomes narrow. That is, the interval required for focus adjustment is insufficient.

Further, the position of the focusing range is farther from the perspective objective optical system than the position of the preferable range. In this case, the position of the near point in the focusing range is farther from the perspective objective optical system than the position of the near point in the preferable range. Therefore, it becomes difficult to form an image of an object located at a near point in a preferable range in an in-focus state.

Further, if the refractive power of the rear lens group becomes too large, the refractive power of the positive lenses constituting the rear lens group also increases. In this case, since the radius of curvature of the lens surface becomes small, it becomes difficult to process the lenses constituting the rear lens group.

If the upper limit of the conditional expression (3) is exceeded, the positive refractive power in the rear lens group becomes too small. In this case, the image position is too far from the rear lens group, so that the length of the glass path from the brightness diaphragm to the image position becomes long. As a result, the total length of the optical system becomes long. In addition, the entire optical system becomes large.

Further, the position of the focusing range is closer to the perspective objective optical system than the position of the preferable range. In this case, the position of the far point in the focusing range is closer to the perspective objective optical system than the position of the far point in the preferable range. Therefore, it becomes difficult to form an image of an object located at a far point in a preferable range in an in-focus state.

In addition, coma aberration is greatly generated in the positive direction in the peripheral portion of the image. Therefore, the optical performance is deteriorated.

The perspective objective optical system of the present embodiment preferably satisfies the following conditional expression (4).
-2.8 <fF / f <-1.5 (4)
here,
fF is the focal length of the front lens group,
f is the focal length of the entire perspective objective optical system,
Is.

The conditional expression (4) is a conditional expression that defines the focal length of the front lens group.

When the upper limit of the conditional expression (4) is exceeded, the refractive power of the front lens group becomes large, so that the angle of view of the perspective objective optical system becomes large. As the angle of view increases, the height of light rays in the front lens group increases, so that the outer diameter of the lenses constituting the front lens group increases.

Further, as the angle of view increases, the peripheral portion of the image becomes dark. In this case, even in the observation image obtained by the image pickup by the image pickup element, the peripheral portion becomes dark. In order to brighten the peripheral part of the image, the illumination light that illuminates the peripheral part of the observation range must be further brightened. Then, the size of the illumination optical system will be increased.

The front lens group consists of a front negative lens. Therefore, as the refractive power of the front lens group increases, the refractive power of the front negative lens increases. In this case, especially in the case of the front negative lens, the radius of curvature of the lens surface becomes small, which makes it difficult to process the front negative lens.

Further, when the refractive power of the front negative lens becomes large, the aberration generated in the front negative lens becomes large, so that the aberration of the entire optical system is deteriorated. In order to correct the aberration generated by the front negative lens, it is necessary to increase the number of lenses constituting the front lens group. However, if the number of lenses is increased, the optical system becomes large.

As described above, if the upper limit value of the conditional expression (4) is exceeded, the size of the perspective objective optical system and the size of the illumination optical system are increased. The perspective objective optical system is arranged at the tip of the endoscope together with the illumination optical system. Therefore, exceeding the upper limit of the conditional expression (4) is not preferable for reducing the diameter of the tip of the endoscope.

Further, when the refractive power of the front negative lens becomes large, the deterioration of the optical performance becomes large especially when the front negative lens is eccentric. As a result, it becomes difficult to realize a perspective objective optical system having stable optical performance.

When it is less than the lower limit of the conditional expression (4), the refractive power of the front lens group becomes small, so that the angle of view of the perspective objective optical system becomes small. In order to increase the angle of view in this state, the distance from the front negative lens to the brightness aperture must be increased. Then, the height of the light beam between the front negative lens and the brightness diaphragm becomes high, so that the front lens group becomes large and the entire optical system becomes large.

The perspective objective optical system of the present embodiment preferably satisfies the following conditional expression (5).
4.0 <f3 / f <8.0 (5)
here,
f3 is the focal length of the junction lens,
f is the focal length of the entire perspective objective optical system,
Is.

The conditional expression (5) is a conditional expression that defines the focal length of the junction lens.

If it is less than the lower limit of the conditional expression (5), the focal length of the junction lens becomes too small. That is, the positive refractive power of the junction lens becomes too large. In this case, the image position gets too close to the rear lens group, so that the interval required for focus adjustment becomes narrow. That is, the interval required for focus adjustment is insufficient.

Further, the position of the focusing range is farther from the perspective objective optical system than the position of the preferable range. In this case, the position of the near point in the focusing range is farther from the perspective objective optical system than the position of the near point in the preferable range. Therefore, it becomes difficult to form an image of an object located at a near point in a preferable range in an in-focus state.

Further, coma aberration is greatly generated in the negative direction in the peripheral portion of the image. Therefore, the optical performance is deteriorated.

Further, for example, when the junction lens has a positive lens and a negative lens, the balance between the refractive power of the entire positive lens and the refractive power of the entire negative lens in the rear lens group is lost. As a result, axial chromatic aberration and chromatic aberration of magnification occur. Therefore, the optical performance is deteriorated. When used with an image sensor with a small pixel pitch, the effect on the deterioration of optical performance is significant.

Further, if the refractive power of the bonded lens becomes too large, the radius of curvature of the lens surface becomes small, which makes it difficult to process the lens constituting the bonded lens. When the junction lens has a positive lens and a negative lens, both the positive lens processing and the negative lens processing become difficult.

If the upper limit of the conditional expression (5) is exceeded, the focal length of the junction lens becomes too long. That is, the positive refractive power of the junction lens becomes too small. In this case, the image position is too far from the rear lens group, so that the length of the glass path from the brightness diaphragm to the image position becomes long. As a result, the total length of the optical system becomes long. In addition, the entire optical system becomes large.

Further, the position of the focusing range is closer to the perspective objective optical system than the position of the preferable range. In this case, the position of the far point in the focusing range is closer to the perspective objective optical system than the position of the far point in the preferable range. Therefore, it becomes difficult to form an image of an object located at a far point in a preferable range in an in-focus state.

In addition, coma aberration is greatly generated in the positive direction in the peripheral portion of the image. Therefore, the optical performance is deteriorated.

When the junction lens has a positive lens and a negative lens, the balance between the refractive power of the entire positive lens and the refractive power of the entire negative lens in the rear lens group is lost. As a result, axial chromatic aberration and chromatic aberration of magnification occur. Therefore, the optical performance is deteriorated. When used with an image sensor having a small pixel pitch of the image sensor, the effect on the deterioration of optical performance is significant.

The perspective objective optical system of the present embodiment preferably satisfies the following conditional expression (6).
3.5 <D1 / f <8.0 (6)
here,
D1 is the air equivalent length from the image side of the front negative lens to the brightness aperture.
f is the focal length of the entire perspective objective optical system,
Is.

The conditional expression (6) is a conditional expression that defines the air conversion length from the image side surface of the front negative lens to the brightness diaphragm. For example, in Example 1 described later, D1 can be obtained by the following equation.
D1 = d2 + d3 / n3 + d4 + d5 / n5 + d6

If it is less than the lower limit of the conditional expression (6), it becomes difficult to secure a sufficient space for arranging the optical path conversion element having the optimum outer diameter shape. Therefore, the optical path conversion element causes the light beam to be eclipsed. In addition, there is a risk that flare will occur in the image due to the incident light rays on the optical path other than the optical surface of the optical path conversion element.

In addition, it becomes difficult to appropriately secure the length of the frame member that holds the front lens group. In this case, the frame member cannot be stably held by the jig for assembly. Therefore, it becomes difficult to assemble the perspective objective optical system and adjust the focus with high accuracy. Further, it becomes difficult to attach and fix the perspective objective optical system to the tip of the endoscope with high accuracy.

If the upper limit of the conditional expression (6) is exceeded, a sufficient space for arranging the optical path conversion element can be secured, but the glass path length from the front negative lens to the brightness diaphragm becomes too long. In this case, the height of the light beam in the front negative lens is high, so that the outer diameter of the front negative lens is large. Along with this, the perspective objective optical system becomes larger. Further, as the size of the perspective objective optical system increases, the outer diameter of the endoscope on which the perspective objective optical system is mounted also increases.

The perspective objective optical system of the present embodiment preferably satisfies the following conditional expression (7).
1.5 <D2 / f <2.5 (7)
here,
D2 is the air equivalent length from the image side to the image plane of the final lens of the rear lens group.
f is the focal length of the entire perspective objective optical system,
Is.

The conditional expression (7) is a conditional expression that defines the air conversion length from the image side surface to the image plane of the final lens of the rear lens group. Here, the final lens means a lens having a refractive power. Therefore, a parallel plate filter such as a color filter or a powerless lens is not the final lens. For example, in Example 1 described later, D2 can be obtained by the following equation.
D2 = d14 + d15 / n15 + d16 / n16 + d17 / n17 + d18 / n18 + d19

If it falls below the lower limit of the conditional expression (7), the distance from the final lens to the image plane becomes too narrow.
In this case, the distance between the image sensor and the perspective objective optical system becomes too narrow, so that sufficient focus adjustment cannot be performed when assembling the perspective objective optical system.

Further, the position of the focusing range is closer to the perspective objective optical system than the position of the preferable range. In this case, the position of the far point in the focusing range is closer to the perspective objective optical system than the position of the far point in the preferable range. Therefore, it becomes difficult to form an image of an object located at a far point in a preferable range in an in-focus state.

If the upper limit of the conditional expression (7) is exceeded, a sufficient distance from the final lens to the image plane can be secured, so that the focus can be adjusted at the time of assembling the perspective objective optical system. However, since the distance from the final lens to the image plane becomes too long, the position of the image sensor is too far from the perspective objective optical system. As a result, when the perspective objective optical system is attached to the tip of the endoscope, the perspective objective optical system and the image pickup element (hereinafter referred to as “imaging system”) tend to interfere with other members. In order to avoid this interference, it is necessary to provide a clearance around the imaging system in the endoscope. Then, the entire tip of the endoscope becomes large.

The perspective objective optical system of the present embodiment preferably satisfies the following conditional expression (8).
-0.9 <fF / fR <-0.5 (8)
here,
fF is the focal length of the front lens group,
fR is the focal length of the rear lens group,
Is.

The conditional expression (8) is a conditional expression that defines the ratio of the focal length of the front lens group to the focal length of the rear lens group. By satisfying the conditional equation (8), the balance between the refractive power of the front lens group and the refractive power of the rear lens group can be optimized. As a result, it is possible to realize a perspective objective optical system in which various aberrations are well corrected.

When the upper limit of the conditional expression (8) is exceeded, the focal length of the front lens group becomes smaller. That is, the refractive power of the front lens group increases. Therefore, the angle of view of the perspective objective optical system becomes large. As the angle of view increases, the height of the light rays passing through the lens increases, so that the outer diameter of the lenses constituting the front lens group increases.

Further, as the angle of view increases, the peripheral portion of the image becomes dark. In this case, even in the observation image obtained by the image pickup by the image pickup element, the peripheral portion becomes dark. In order to brighten the peripheral part of the image, the illumination light that illuminates the peripheral part of the observation range must be further brightened. This will lead to an increase in the size of the illumination optical system.

As described above, if the upper limit value of the conditional expression (8) is exceeded, the size of the perspective objective optical system and the size of the illumination optical system are increased. The perspective objective optical system and the illumination optical system are arranged at the tip of the endoscope. Therefore, exceeding the upper limit of the conditional expression (8) is not preferable for reducing the diameter of the endoscope.

Since the front lens group is composed of a front negative lens, the refractive power of the front negative lens increases as the refractive power of the front lens group increases. In this case, the refractive power of the front negative lens is larger than the positive refractive power of the rear lens group. Therefore, the aberration affected by the negative refractive power cannot be sufficiently corrected by the rear lens group. As a result, curvature of field occurs in the positive direction.

Further, the balance between the refractive power of the front lens group and the refractive power of the rear lens group becomes poor. In this case, since the amount of astigmatism generated becomes large, the image plane in the meridian direction is greatly tilted in the positive direction. Therefore, when the lens is eccentric, one-sided blur is likely to occur in the image. In particular, there is a risk that the peripheral portion of the image will be significantly blurred during near-point observation.

In addition, even in the observation image obtained by imaging with the image sensor, one-sided blur is likely to occur. In particular, there is a risk that the peripheral portion of the observed image will be significantly blurred during near-point observation.

Below the lower limit of the conditional expression (8), the focal length of the front lens group becomes long. That is, the refractive power of the front lens group becomes small. Therefore, the angle of view of the perspective objective optical system becomes small.

Further, the refractive power of the front negative lens is smaller than the positive refractive power of the rear lens group. Therefore, the correction by the rear lens group becomes excessive for the aberration affected by the negative refractive power. As a result, a large curvature of field occurs in the negative direction.

Further, the balance between the refractive power of the front lens group and the refractive power of the rear lens group becomes poor. In this case, since the amount of astigmatism generated becomes large, the image plane in the meridian direction is greatly tilted in the negative direction. Therefore, when the lens is eccentric, one-sided blur is likely to occur in the image. In particular, there is a risk that the peripheral portion of the image will be significantly blurred during apogee observation.

In addition, even in the observation image obtained by imaging with the image sensor, one-sided blur is likely to occur. In particular, when observing at a long point, there is a risk that the peripheral portion of the observed image will be significantly blurred.

In the perspective objective optical system of the present embodiment, the rear positive lens has a surface having a small radius of curvature facing the image side, and the junction lens has a surface having a small radius of curvature facing the object side. It is preferable to satisfy (9).
0.4 << R3 / R2 | <0.85 (9)
here,
R2 is the radius of curvature of the image side of the rear positive lens,
R3 is the radius of curvature of the side surface of the object of the bonded lens,
Is.

The conditional expression (9) is a conditional expression that defines the radius of curvature of the image side surface of the rear positive lens and the radius of curvature of the object side surface of the bonded lens. By satisfying the conditional equation (9), the balance between the refractive power of the image side surface of the rear positive lens and the refractive power of the object side surface of the junction lens can be optimized.

If it is less than the lower limit of the conditional expression (9), the radius of curvature of the side surface of the object of the junction lens becomes too small, and the light beam passing through this surface is greatly bent. In this case, the angle of light ray incident on the image plane becomes smaller. Therefore, the angle of the light beam emitted from the perspective objective optical system cannot be set to an angle that satisfies the oblique incident characteristics of the image pickup device. As a result, the efficiency of incident light rays on the image sensor deteriorates, so that the peripheral portion of the image becomes dark.

In addition, since the image position is too close to the rear lens group, the interval required for focus adjustment is insufficient.

If the upper limit of the conditional expression (9) is exceeded, the radius of curvature of the image side surface of the rear positive lens becomes too small, and the light beam passing through this surface is greatly bent. In this case, the angle of light ray incident on the image plane becomes smaller. Therefore, the angle of the light beam emitted from the perspective objective optical system cannot be set to an angle that satisfies the oblique incident characteristics of the image pickup device. As a result, the efficiency of incident light rays on the image sensor deteriorates, so that the peripheral portion of the image becomes dark.

Further, since the image position is too close to the rear lens group, the interval required for focus adjustment is insufficient.

Further, in the perspective objective optical system of the present embodiment, the optical path conversion element is preferably a prism or a mirror.

Further, in the perspective objective optical system of the present embodiment, a high refractive index glass material can be used for the optical path conversion element.

As described above, in the perspective objective optical system of the present embodiment, the optical path conversion element is arranged on the object side of the brightness diaphragm. However, in this configuration, the glass path length from the front negative lens to the brightness diaphragm is longer than in the case where the optical path conversion element is arranged on the image side of the brightness diaphragm. In this case, since the light beam height is particularly high in the front negative lens, the outer diameter of the front negative lens tends to be large.

Therefore, it is preferable to use a high refractive index glass material for the optical path conversion element. By doing so, the air conversion length of the optical path conversion element can be reduced, so that the glass path length from the front negative lens to the brightness diaphragm is shortened. In this case, since the height of the light beam in the front negative lens can be suppressed to a low value, the outer diameter of the front negative lens can be reduced.

However, the refractive index of the glass material used for the optical path conversion element cannot be simply increased. It is desired that the perspective objective optical system can observe a wider range. In order to meet this demand, it is necessary to widen the optical system. The angle of view of the optical system is mainly determined by the refractive power of the negative lens located on the object side. Therefore, in order to secure a wide angle of view in the perspective objective optical system of the present embodiment, the refractive power of the front negative lens becomes large.

When the refractive power of the front negative lens becomes large, the radius of curvature of the image side surface of the front negative lens becomes small, and the lens workability deteriorates. Further, the front negative lens is held by the objective frame. When the refractive power of the front negative lens increases, the declination and one-sided blur due to the eccentricity between the objective frame and the front negative lens increase, so the declination has a large effect on the optical performance and the one-sided blur has a large effect on the optical performance. Become.

Therefore, in the perspective objective optical system of the present embodiment, the length of the glass path from the front negative lens to the brightness aperture is slightly lengthened to slightly weaken the refractive power of the front negative lens. As described above, the air conversion length of the optical path conversion element, that is, the refractive index of the glass material used for the optical path conversion element affects the glass path length from the front negative lens to the brightness diaphragm. Therefore, when setting the refractive index of the glass material used for the optical path conversion element, it is necessary to consider the refractive power of the front negative lens.

In this way, the refractive index of the glass material used for the optical path conversion element is appropriately set in consideration of not only the outer diameter of the front negative lens but also the refractive power of the front negative lens (the effect of the eccentricity of the lens on the optical performance). There is a need to. The perspective objective optical system of the present embodiment has a high refractive index so that the glass path length from the front negative lens to the brightness aperture is optimized in consideration of the front negative lens outer diameter and the refractive power of the front negative lens. A glass material is used for the optical path conversion element.

Further, in the perspective objective optical system of the present embodiment, a low-dispersion glass material can be used for the positive lens of the bonded lens, and a high-dispersion glass material can be used for the negative lens of the bonded lens.

In general, the Abbe number of the high refractive index glass material is not so large, so that the dispersion is large in the high refractive index glass material. Therefore, even if the air conversion length of the optical path conversion element can be reduced by using a high-refractive index glass material for the optical path conversion element, the influence on chromatic aberration remains.

For this reason, it is preferable to use a low-dispersion glass material for the positive lens of the junction lens and a high-dispersion glass material for the negative lens of the junction lens. In particular, it is preferable to use a glass material having anomalous dispersibility for the negative lens of the junction lens. By doing so, chromatic aberration can be satisfactorily corrected. Further, various aberrations in the entire perspective objective optical system can be in a balanced state.

In order to satisfactorily correct chromatic aberration, it is particularly preferable to use a glass material having an Abbe number of 60 or more for the positive lens of the junction lens and a glass material having an Abbe number of 20 or less for the negative lens.

Further, the perspective endoscope of the present embodiment is characterized by including the above-mentioned perspective objective optical system.

The perspective objective optical system of the present embodiment is a compact and high-performance perspective objective optical system. Therefore, by providing such a squint objective optical system, it is possible to obtain a high-quality image and realize a squint endoscope having a reduced-diameter tip portion.

Further, the perspective objective optical system of the present embodiment can be used for an endoscope device. The endoscope device includes at least the perspective objective optical system of the present embodiment and an image pickup device.

Prior to the description of the embodiment, the outline of the perspective objective optical system of the present embodiment will be described. In the lens cross-sectional view of each embodiment, the optical path conversion element is shown as an expanded view of a prism. Therefore, the optical path conversion element is drawn as a parallel flat plate. In the description of the perspective objective optical system of the present embodiment, a prism in an unexpanded state is used.

FIG. 3 shows an example of an unexpanded prism. FIG. 3 is a cross-sectional view of the lens when the prism is drawn without being expanded. Here, as the perspective objective optical system of the present embodiment, the perspective objective optical system of Example 1 is exemplified. The perspective objective optical system has an anterior lens group GF and a posterior lens group GR arranged via a prism P, and a brightness aperture S is arranged between the prism P and the posterior lens group GR. ..

That is, in the perspective objective optical system of the present embodiment, the front lens group GF is arranged on the object side of the prism P, and the rear lens group GR is arranged on the image side of the prism P. The front lens group GF has a negative refractive power and is composed of the front negative lens L1. The rear lens group GR has a positive refractive power, and is composed of a rear positive lens L2 and a junction lens CL having a positive refractive power. In the bonded lens CL, the positive lens L3 and the negative lens L4 are sequentially bonded.

If the prism P drawn as a parallel flat plate is configured as a single-reflection prism, a lateral viewing objective optical system capable of 90-degree lateral observation can be configured as shown in FIG. Further, if the reflecting surface of the prism is set to an angle other than 45 degrees, an objective optical system such as forward vision or rear vision other than 45 degrees can be configured. Further, if it is configured as a double-reflection type prism, a 45-degree forward-viewing objective optical system can be configured.

Further, the prism P can be composed of a plurality of prisms. FIG. 4A shows a configuration in which two prisms can be viewed sideways, and FIG. 4B shows a configuration in which two prisms can be viewed forward.

Further, it is preferable to use a high refractive index glass material as the glass material of the prism P. By doing so, since the air-equivalent length of the prism P can be reduced, both the outer shape and the refractive power of the front negative lens L1 can be reduced while ensuring a wide angle of view.

By using a high refractive index glass material having a refractive index of 1.8 or more for the glass material of the prism P, the air equivalent length of the prism P can be further reduced. However, since the high refractive index glass material has a small Abbe number, the color dispersion effect is large. Therefore, the color dispersion effect of the prism P becomes large.

On the other hand, since the low refractive index glass material has a large Abbe number, the color dispersion effect can be suppressed to a small level. By using a low refractive index glass material having a refractive index of about 1.5 as the glass material of the prism P, the color dispersion effect of the prism P can be suppressed. However, since the air-equivalent length of the prism P becomes small, the glass path length from the front negative lens L1 to the brightness diaphragm S becomes substantially short. As a result, the refractive power of the front negative lens L1 increases.

When the refractive power of the front negative lens L1 becomes large, performance deterioration due to eccentricity between the objective frame and the front negative lens L1 tends to occur. On the other hand, if the refractive power of the front negative lens L1 is reduced, the influence of the eccentricity of the front negative lens can be suppressed, but the outer diameter of the front negative lens L1 becomes large. Therefore, it is necessary to configure the entire perspective objective optical system while satisfying the required optical performance and considering the influence of the outer diameter of the front negative lens L1 and the eccentricity of the front negative lens L1.

The glass material of the front negative lens L1 may be used as sapphire. Since sapphire is a material with extremely high hardness, it is resistant to external impact. Therefore, the lens surface on the object side is less likely to be scratched. By using sapphire, it is less likely that scratches will be reflected on the image and flare will occur due to the scratches.

The glass material of the front negative lens L1 is not limited to sapphire. If a high-hardness crystal material is used for the front negative lens L1, the surface of the lens is less likely to be scratched.

A rear positive lens L2 is used for the rear lens group of the perspective objective optical system of this embodiment. In FIG. 3, a biconvex positive lens is used for the rear positive lens L2. Since the refractive index of the low-dispersion glass material is low, when the low-dispersion glass material is used for the rear positive lens L2, the radius of curvature of the lens surface becomes small. Therefore, there tends to be a problem that a sufficient edge thickness of the lens cannot be secured and a problem that a lens outer diameter having a margin for the effective aperture cannot be secured.

Therefore, in consideration of the processability of the lens, it is preferable that the radius of curvature of the lens surface of the rear positive lens L2 does not become too small. Therefore, it is preferable to use a glass material having a refractive index of 1.6 or more for the rear positive lens L2.

When the rear positive lens L2 is composed of a biconvex lens, the absolute value of the radius of curvature on the side surface of the object may be larger than the absolute value of the radius of curvature on the side surface of the image. By doing so, aberration correction can be easily performed.

Further, as the pixel pitch of the image pickup device becomes smaller, it is necessary to suppress the chromatic aberration to be small. In order to cope with this, it is preferable to use a highly dispersed glass material having a refractive index of 1.9 or more and an Abbe number of 25 or less for the negative lens L4 constituting the junction lens CL. By doing so, it is possible to improve the correction of chromatic aberration.

On the other hand, for the positive lens L3 constituting the junction lens CL, it is preferable to use a low-dispersion glass material having a large Abbe number as much as possible. For example, it is preferable to use a glass material having an Abbe number of 45 or more for the positive lens L3.

Further, by arranging the junction lens CL at a position close to the image plane, the height of the light beam passing through the junction lens CL becomes high. By locating the junction lens CL at a position where the light beam height is high, the chromatic aberration of magnification can be satisfactorily corrected. As described above, arranging the junction lens CL at a position close to the image plane is particularly effective for correcting chromatic aberration of magnification.

Further, the parallel flat plate other than the prism provided in the perspective objective optical system of this embodiment is, for example, an infrared cut filter or a color temperature conversion filter. These filters are used for sensitivity correction and color correction of an image pickup device such as a CCD.

Further, a laser cut filter or a special function filter may be arranged in the perspective objective optical system. As the laser cut filter, for example, there is a filter for cutting laser light such as a YAG laser or a semiconductor laser. As a special function filter, for example, there is a notch filter that cuts light rays in a specific wavelength range.

Further, as the optical filter, an absorption type filter, a reflection type filter, or a composite type thereof may be used. Further, a filter provided with an antireflection film may be used.

Further, it is also possible to provide an interference film having infrared cut characteristics or laser light cut characteristics on the transmission surface of the prism.

Further, the parallel plate filters arranged on the image plane side of the perspective objective optical system of this embodiment are a glass lid GL used for the image pickup device and a cover glass CG provided on the front side thereof. By holding the side surface and the surface of the cover glass CG with the frame member, the image pickup element is fixed in the frame member.

For miniaturization, the glass lid GL can be directly held without providing the cover glass CG.

Further, the image plane I of the perspective objective optical system and the light receiving surface of the image sensor ID are configured to coincide with each other.

Further, a filter can be provided in the vicinity of the front negative lens L1 to reduce the volume of the air layer formed on the image plane side of the front negative lens L1. As a result, the influence of fogging due to dew condensation on the lens surface can be reduced.

Further, the front negative lens L1 and the filter may be joined, or both may be hermetically sealed with solder or the like. By doing so, it is possible to prevent fogging more effectively.

Although the number of lenses of the perspective objective optical system of this embodiment is as small as 4, the imaging performance is good. As described above, in the perspective objective optical system of the present embodiment, the objective optical system can be configured with a small number of lenses, so that the cost can be reduced.

Further, in the perspective objective optical system of the present embodiment, the air spacing is narrower than that of the conventional perspective objective optical system, so that the entire optical system is smaller.

The drawings will be described. In each of the drawings of Examples 1 to 19, (a) shows a cross-sectional view of a perspective objective optical system. P represents a prism, F1 represents a filter, CG represents a cover glass, GL represents a glass lid, and I represents an image plane.

The aberration diagram will be described. (B) shows spherical aberration (SA), (c) shows astigmatism (AS), (d) shows distortion (DT), and (e) shows chromatic aberration of magnification (CC).

In each aberration diagram, the horizontal axis represents the amount of aberration. For spherical aberration, astigmatism, and magnification aberration, the unit of aberration amount is mm. For distortion, the unit of aberration amount is%. Further, IH is the image height, the unit is mm, and Fno is the F number. The unit of wavelength of the aberration curve is nm.

Hereinafter, each embodiment will be described.

(Example 1)
The perspective objective optical system according to the first embodiment will be described. The perspective objective optical system of the first embodiment has a front lens group GF having a negative refractive power, an optical path conversion element P, a brightness aperture S, and a rear lens group GR having a positive refractive power in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side. The magnitude of the radius of curvature of the lens surface is compared by an absolute value. The same applies to Examples 2 to 19.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A filter F2, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F2 is arranged between the biconvex positive lens L2 and the junction lens.

(Example 2)
The perspective objective optical system according to the second embodiment will be described. In the perspective objective optical system of the second embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A cover glass CG and a glass lid GL are arranged in the rear lens group GR.

(Example 3)
The perspective objective optical system according to the third embodiment will be described. In the perspective objective optical system of the third embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A filter F2, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F2 is arranged between the biconvex positive lens L2 and the junction lens.

(Example 4)
The perspective objective optical system according to the fourth embodiment will be described. The perspective objective optical system of the fourth embodiment has a front lens group GF having a negative refractive power, an optical path conversion element P, a brightness aperture S, and a rear lens group GR having a positive refractive power in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A filter F2, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F2 is arranged between the biconvex positive lens L2 and the junction lens.

(Example 5)
The perspective objective optical system according to the fifth embodiment will be described. In the perspective objective optical system of the fifth embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a biconcave negative lens L4. Here, the biconvex positive lens L3 and the biconcave negative lens L4 form a bonded lens having a positive refractive power.

The positive meniscus lens L2 has a surface having a small radius of curvature facing the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A filter F2, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F2 is arranged between the positive meniscus lens L2 and the junction lens.

(Example 6)
The perspective objective optical system according to the sixth embodiment will be described. In the perspective objective optical system of the sixth embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The positive meniscus lens L2 has a surface having a small radius of curvature facing the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A cover glass CG and a glass lid GL are arranged in the rear lens group GR.

(Example 7)
The perspective objective optical system according to the seventh embodiment will be described. In the perspective objective optical system of the seventh embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A cover glass CG and a glass lid GL are arranged in the rear lens group GR.

(Example 8)
The perspective objective optical system according to the eighth embodiment will be described. In the perspective objective optical system of the eighth embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A cover glass CG and a glass lid GL are arranged in the rear lens group GR.

(Example 9)
The perspective objective optical system according to the ninth embodiment will be described. In the perspective objective optical system of the ninth embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a biconcave negative lens L4. Here, the biconvex positive lens L3 and the biconcave negative lens L4 form a bonded lens having a positive refractive power.

The positive meniscus lens L2 has a surface having a small radius of curvature facing the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A cover glass CG and a glass lid GL are arranged in the rear lens group GR.

(Example 10)
The perspective objective optical system according to the tenth embodiment will be described. In the perspective objective optical system of the tenth embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A cover glass CG and a glass lid GL are arranged in the rear lens group GR.

(Example 11)
The perspective objective optical system according to the eleventh embodiment will be described. In the perspective objective optical system of the eleventh embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A low refractive index glass material having a refractive index of about 1.5 is used for the optical path conversion element P. Since the Abbe number is as large as 60 or more, the color dispersion effect of the prism is suppressed as compared with the high refractive index glass material.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The positive meniscus lens L2 has a surface having a small radius of curvature facing the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A cover glass CG and a glass lid GL are arranged in the rear lens group GR.

(Example 12)
The perspective objective optical system according to the twelfth embodiment will be described. In the perspective objective optical system of the twelfth embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A low refractive index glass material having a refractive index of about 1.5 is used for the optical path conversion element P. Since the Abbe number is as large as 60 or more, the color dispersion effect of the prism is suppressed as compared with the high refractive index glass material.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The positive meniscus lens L2 has a surface having a small radius of curvature facing the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A cover glass CG and a glass lid GL are arranged in the rear lens group GR.

(Example 13)
The perspective objective optical system according to the thirteenth embodiment will be described. In the perspective objective optical system of the thirteenth embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A low refractive index glass material having a refractive index of about 1.5 is used for the optical path conversion element P. Since the Abbe number is as large as 60 or more, the color dispersion effect of the prism is suppressed as compared with the high refractive index glass material.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The positive meniscus lens L2 has a surface having a small radius of curvature facing the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A filter F2, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F2 is arranged between the positive meniscus lens L2 and the junction lens.

(Example 14)
The perspective objective optical system according to the fourteenth embodiment will be described. In the perspective objective optical system of Example 14, in order from the object side, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A low refractive index glass material having a refractive index of about 1.5 is used for the optical path conversion element P. Since the Abbe number is as large as 60 or more, the color dispersion effect of the prism is suppressed as compared with the high refractive index glass material.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The positive meniscus lens L2 has a surface having a small radius of curvature facing the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 is arranged in the front lens group GF. The filter F1 is arranged between the plano-concave negative lens L1 and the optical path conversion element P. A filter F2, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F2 is arranged between the positive meniscus lens L2 and the junction lens.

(Example 15)
The perspective objective optical system according to the fifteenth embodiment will be described. In the perspective objective optical system of the fifteenth embodiment, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power are arranged in order from the object side. And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The positive meniscus lens L2 has a surface having a small radius of curvature facing the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 and a filter F2 are arranged in the front lens group GF. The filter F1 and the filter F2 are arranged between the planing negative lens L1 and the optical path conversion element P. A filter F3, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F3 is arranged between the positive meniscus lens L2 and the junction lens.

(Example 16)
The perspective objective optical system according to the sixteenth embodiment will be described. In the perspective objective optical system of Example 16, in order from the object side, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The positive meniscus lens L2 has a surface having a small radius of curvature facing the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 and a filter F2 are arranged in the front lens group GF. The filter F1 and the filter F2 are arranged between the planing negative lens L1 and the optical path conversion element P. A filter F3, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F3 is arranged between the positive meniscus lens L2 and the junction lens.

(Example 17)
The perspective objective optical system according to the seventeenth embodiment will be described. In the perspective objective optical system of Example 17, in order from the object side, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 and a filter F2 are arranged in the front lens group GF. The filter F1 and the filter F2 are arranged between the planing negative lens L1 and the optical path conversion element P. A filter F3, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F3 is arranged between the biconvex positive lens L2 and the junction lens.

(Example 18)
The perspective objective optical system according to the eighteenth embodiment will be described. In the perspective objective optical system of Example 18, in order from the object side, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 and a filter F2 are arranged in the front lens group GF. The filter F1 and the filter F2 are arranged between the planing negative lens L1 and the optical path conversion element P. A filter F3, a cover glass CG, and a glass lid GL are arranged in the rear lens group GR. The filter F3 is arranged between the biconvex positive lens L2 and the junction lens.

(Example 19)
The perspective objective optical system according to the nineteenth embodiment will be described. In the perspective objective optical system of Example 19, in order from the object side, the front lens group GF having a negative refractive power, the optical path conversion element P, the brightness aperture S, and the rear lens group GR having a positive refractive power And consists of.

The front lens group GF is composed of a plano-concave negative lens L1 whose object side is a flat surface.

The optical path conversion element P is arranged between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high-refractive index glass material having a refractive index of 1.8 or more is used for the optical path conversion element P.

The brightness diaphragm S is arranged between the optical path conversion element P and the rear lens group GR. More specifically, the brightness diaphragm S is provided on the image side surface of the optical path conversion element P.

The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 with a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a junction lens having a positive refractive power.

The biconvex positive lens L2 faces a surface having a small radius of curvature toward the image plane side. The junction lens has a surface having a small radius of curvature facing the object surface side.

A filter F1 and a filter F2 are arranged in the front lens group GF. The filter F1 and the filter F2 are arranged between the planing negative lens L1 and the optical path conversion element P. A cover glass CG and a glass lid GL are arranged in the rear lens group GR.

The perspective objective optical system according to this embodiment is a bright and high-performance perspective objective optical system having an F number of about 3 while supporting a wide angle of view such as 100 to 140 degrees. ..

As described above, the perspective objective optical system of each embodiment has a front lens group arranged on the object side of the prism and a rear lens group arranged on the image side of the prism, and has a front lens group. Has a negative refractive power and is composed of a front negative lens, and a rear lens group is composed of a rear positive lens and a junction lens having a positive refractive power, and is bright. A narrow aperture is provided between the prism and the rear lens group.

The perspective objective optical system of each embodiment has an optimum lens configuration in which the optical performance is improved in response to the miniaturization and the increase in the number of pixels of the image pickup device, and the diameter of the tip of the endoscope is reduced by this configuration. Can also contribute to. Further, since the perspective objective optical system of each embodiment satisfies each conditional expression, various aberrations are satisfactorily corrected.

The numerical data of each of the above Examples is shown below. In the surface data, r is the radius of curvature of each surface, d is the wall thickness or air spacing of each optical member, nd is the refractive index of each optical member with respect to the d line, and νd is the Abbe number with respect to the d line of each optical member. In various data, IH is the image height, ω is the half angle, Fno is the F number of the perspective objective optical system, f is the focal distance of the entire perspective objective optical system, f2 is the focal distance of the rear positive lens, and f3 is. FR is the focal distance of the rear lens group, fF is the focal distance of the front lens group, D1 is the air equivalent length from the image side of the front negative lens to the brightness aperture, and D2 is. The air equivalent length from the image side surface to the image plane of the final lens of the rear lens group, R2 represents the radius of curvature of the image side surface of the rear positive lens, and R3 represents the radius of curvature of the object side surface of the junction lens. The unit of r, d, IH, air conversion length and each focal length is mm, and the unit of the half angle of view ω is °. Further, f is standardized to 1 mm.

Numerical Example 1
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.7564 1.88300 40.76
2 1.6000 1.2668
3 ∞ 0.7564 1.51633 64.14
4 ∞ 0.0756
5 ∞ 4.3816 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2458
8 13.7053 1.8742 1.80440 39.59
9 -5.0830 0.1135
10 ∞ 0.7564 1.49400 75.00
11 ∞ 0.2843
12 3.4026 2.2065 1.81600 46.62
13 -1.9755 0.6178 1.92286 18.90
14 -140.6763 0.9315
15 ∞ 0.8510 1.51633 64.14
16 ∞ 0.0189 1.51300 64.00
17 ∞ 0.6619 1.50510 63.26
18 ∞ 0
(Image plane) ∞

Various data IH 0.764
ω 49.391
Fno 2.972
f 1
f2 4.824
fR 2.678
fF -1.812
f3 4.861
D1 4.168
D2 1.945

Numerical Example 2
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.7602 1.88300 40.76
2 1.6454 1.2746
3 ∞ 0.7602 1.49400 75.00
4 ∞ 0.0760
5 ∞ 4.4033 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2470
8 16.6488 1.8025 1.78590 44.20
9 -4.9572 1.4197
10 3.3971 2.2235 1.81600 46.62
11 -2.0221 0.6323 1.92286 18.90
12 -26.4408 0.8774
13 ∞ 0.8552 1.51633 64.14
14 ∞ 0.0190 1.51300 64.00
15 ∞ 0.6651 1.50510 63.26
16 ∞ 0
(Image plane) ∞

Various data IH 0.768
ω 50.061
Fno 2.91
f 1
f2 5.046
fR 2.847
fF -1.863
f3 4.44
D1 4.198
D2 1.896

Numerical Example 3
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.7575 1.88300 40.76
2 1.5860 1.1565
3 ∞ 0.7575 1.51633 64.14
4 ∞ 0.0758
5 ∞ 4.3881 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2462
8 14.0674 1.9849 1.83400 37.16
9 -5.2264 0.1136
10 ∞ 0.7575 1.49400 75.00
11 ∞ 0.1337
12 3.4747 2.0732 1.81600 46.62
13 -2.0212 0.6210 1.92286 18.90
14 -60.0097 1.0559
15 ∞ 0.8522 1.51633 64.14
16 ∞ 0.0189 1.51300 64.00
17 ∞ 0.6629 1.50510 63.26
18 ∞ 0
(Image plane) ∞

Various data IH 0.765
ω 49.38
Fno 2.841
f 1
f2 4.793
fR 2.652
fF -1.796
f3 4.844
D1 4.062
D2 2.071

Numerical Example 4
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.7564 1.88300 40.76
2 1.6000 1.2668
3 ∞ 0.7564 1.51633 64.14
4 ∞ 0.0756
5 ∞ 4.3816 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2458
8 13.7053 1.8742 1.80440 39.59
9 -5.0830 0.1135
10 ∞ 0.7564 1.49400 75.00
11 ∞ 0.2843
12 3.4026 2.2065 1.81600 46.62
13 -1.9755 0.6178 1.92286 18.90
14 -140.6763 0.9315
15 ∞ 0.8510 1.51633 64.14
16 ∞ 0.0189 1.51300 64.00
17 ∞ 0.6619 1.50510 63.26
18 ∞ 0
(Image plane) ∞

Various data IH 0.764
ω 47.883
Fno 2.972
f 1
f2 4.824
fR 2.678
fF -1.812
f3 4.861
D1 4.168
D2 1.945

Numerical Example 5
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.8608 1.88300 40.76
2 1.8052 2.0231
3 ∞ 0.8608 1.51633 64.14
4 ∞ 0.0861
5 ∞ 4.9864 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2798
8 -64.9586 1.8411 1.67270 32.10
9 -4.4125 0.1291
10 ∞ 0.8608 1.49400 75.00
11 ∞ 0.1722
12 3.3787 2.6010 1.81600 46.62
13 -2.1443 0.7108 1.92286 18.90
14 103.7037 1.0654
15 ∞ 0.9684 1.51633 64.14
16 ∞ 0.0215 1.51300 64.00
17 ∞ 0.7532 1.50510 63.26
18 ∞ 0
(Image plane) ∞

Various data IH 0.869
ω 61.076
Fno 2.847
f 1
f2 6.952
fR 2.969
fF -2.044
f3 4.907
D1 5.325
D2 2.219

Numerical Example 6
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.9488 1.88300 40.76
2 2.1759 2.8684
3 ∞ 0.9488 1.49400 75.00
4 ∞ 0.0949
5 ∞ 5.4956 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.7828
8 -45.4040 2.0647 1.74951 35.33
9 -6.0187 0.3321
10 3.6104 3.6307 1.78800 47.37
11 -1.9256 0.7122 1.92286 18.90
12 -20.0410 0.8901
13 ∞ 0.8302 1.51633 64.14
14 ∞ 0.0237 1.51300 64.00
15 ∞ 0.8302 1.50510 63.26
16 ∞ 0
(Image plane) ∞

Various data IH 0.958
ω 75.101
Fno 3.094
f 1
f2 9.054
fR 3.205
fF -2.464
f3 4.954
D1 6.517
D2 2.005

Numerical Example 7
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.8941 1.88300 40.76
2 1.8862 2.3248
3 ∞ 0.8941 1.49400 75.00
4 ∞ 0.0894
5 ∞ 5.1793 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.7377
8 22.3930 2.0707 1.74951 35.33
9 -6.3003 0.3129
10 3.2036 3.0310 1.72916 54.68
11 -2.1567 0.6696 1.92286 18.90
12 -124.5527 0.9246
13 ∞ 0.7824 1.51633 64.14
14 ∞ 0.0224 1.51300 64.00
15 ∞ 0.7824 1.50510 63.26
16 ∞ 0
(Image plane) ∞

Various data IH 0.903
ω 65.641
Fno 3.037
f 1
f2 6.77
fR 3.021
fF -2.136
f3 5.63
D1 5.763
D2 1.975

Numerical Example 8
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.9198 1.88300 40.76
2 2.0130 2.3894
3 ∞ 0.9198 1.49400 75.00
4 ∞ 0.0920
5 ∞ 5.3277 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.7077
8 23.3766 2.1237 1.74951 35.33
9 -6.3372 0.3219
10 3.6903 3.0776 1.81600 46.62
11 -2.2970 0.6975 1.95906 17.47
12 -124.4099 0.9125
13 ∞ 0.8048 1.51633 64.14
14 ∞ 0.0230 1.51300 64.00
15 ∞ 0.8048 1.50510 63.26
16 ∞ 0
(Image plane) ∞

Various data IH 0.929
ω 69.048
Fno 3.036
f 1
f2 6.862
fR 3.037
fF -2.28
f3 5.362
D1 5.926
D2 1.993

Numerical Example 9
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.9119 1.88300 40.76
2 2.0010 2.3691
3 ∞ 0.9119 1.49400 75.00
4 ∞ 0.0912
5 ∞ 5.2823 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.7523
8 -178.8595 2.1299 1.80100 34.97
9 -5.7106 0.3192
10 3.4296 3.1866 1.78800 47.37
11 -2.2888 0.6954 1.95906 17.47
12 196.5563 0.9072
13 ∞ 0.7979 1.51633 64.14
14 ∞ 0.0228 1.51300 64.00
15 ∞ 0.7979 1.50510 63.26
16 ∞ 0
(Image plane) ∞

Various data IH 0.921
ω 68.023
Fno 3.056
f 1
f2 7.324
fR 3.01
fF -2.266
f3 5.462
D1 5.876
D2 1.979

Numerical Example 10
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.9241 1.88300 40.76
2 2.0061 2.4018
3 ∞ 0.9241 1.49400 75.00
4 ∞ 0.0924
5 ∞ 5.3528 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.6361
8 48.2189 1.9861 1.64769 33.79
9 -5.0829 0.3234
10 3.6170 3.1463 1.81600 46.62
11 -2.2574 0.6963 1.95906 17.47
12 -326.5107 0.9252
13 ∞ 0.8086 1.51633 64.14
14 ∞ 0.0231 1.51300 64.00
15 ∞ 0.8086 1.50510 63.26
16 ∞ 0
(Image plane) ∞

Various data IH 0.933
ω 69.762
Fno 3.04
f 1
f2 7.205
fR 3.028
fF -2.272
f3 5.302
D1 5.955
D2 2.011

Numerical Example 11
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.9305 1.88300 40.76
2 2.2252 2.4195
3 ∞ 0.9305 1.49400 75.00
4 ∞ 0.0931
5 ∞ 5.3901 1.51633 64.14
6 ∞ 0
7 (Aperture) ∞ 0.5351
8-8.7194 1.2523 1.80518 25.42
9 -4.5264 0.3257
10 2.6229 3.2937 1.65160 58.55
11 -1.6227 0.6967 1.95906 17.47
12 -6.2315 0.8410
13 ∞ 0.8142 1.51633 64.14
14 ∞ 0.0233 1.51300 64.00
15 ∞ 0.8142 1.50510 63.26
16 ∞ 0
(Image plane) ∞

Various data IH 0.94
ω 69.739
Fno 3.045
f 1
f2 10.316
fR 3.069
fF -2.52
f3 4.502
D1 6.69
D2 1.934

Numerical Example 12
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.8813 1.88300 40.76
2 2.1197 2.2871
3 ∞ 0.8813 1.49400 75.00
4 ∞ 0.0881
5 ∞ 5.1052 1.51633 64.14
6 ∞ 0
7 (Aperture) ∞ 0.5068
8 -15.7484 1.2034 1.69895 30.13
9 -4.4326 0.3085
10 2.3055 3.0799 1.58913 61.14
11 -1.4961 0.6603 1.95906 17.47
12 -5.2306 0.7402
13 ∞ 0.7712 1.51633 64.14
14 ∞ 0.0220 1.51300 64.00
15 ∞ 0.7712 1.50510 63.26
16 ∞ 0
(Image plane) ∞

Various data IH 0.89
ω 62.311
Fno 3.084
f 1
f2 8.456
fR 2.974
fF -2.401
f3 4.647
D1 6.332
D2 1.776

Numerical Example 13
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.8720 1.88300 40.76
2 1.9912 2.2638
3 ∞ 0.8720 1.51633 64.14
4 ∞ 0.0872
5 ∞ 5.0512 1.51633 64.14
6 ∞ 0
7 (Aperture) ∞ 0.5014
8 -31.3613 1.1614 1.62004 36.26
9 -4.1050 0.1308
10 ∞ 0.8720 1.49400 75.00
11 ∞ 0.1744
12 2.4489 3.1349 1.58913 61.14
13 -1.6945 0.6534 1.95906 17.47
14 -6.1436 0.7227
15 ∞ 0.7630 1.51633 64.14
16 ∞ 0.0218 1.51300 64.00
17 ∞ 0.7630 1.50510 63.26
18 ∞ 0
(Image plane) ∞

Various data IH 0.881
ω 62.428
Fno 3.234
f 1
f2 7.495
fR 3.123
fF -2.255
f3 4.967
D1 6.257
D2 1.747

Numerical Example 14
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.9185 1.88300 40.76
2 2.1470 2.7770
3 ∞ 0.9185 1.51633 64.14
4 ∞ 0.0919
5 ∞ 5.3206 1.51633 64.14
6 ∞ 0
7 (Aperture) ∞ 0.5282
8 -12.6022 1.3621 1.83400 37.16
9 -4.7377 0.1378
10 ∞ 0.9185 1.49400 75.00
11 ∞ 0.1837
12 2.6101 3.4414 1.58913 61.14
13 -1.7555 0.6881 1.95906 17.47
14 -5.8965 0.7126
15 ∞ 0.8037 1.51633 64.14
16 ∞ 0.0230 1.51300 64.00
17 ∞ 0.8037 1.50510 63.26
18 ∞ 0
(Image plane) ∞

Various data IH 0.928
ω 69.563
Fno 3.034
f 1
f2 8.438
fR 3.296
fF -2.432
f3 5.144
D1 6.984
D2 1.792

Numerical Example 15
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.5780 1.88300 40.78
2 1.5818 1.0156
3 ∞ 0.7707 1.51633 64.14
4 ∞ 0.0578
5 ∞ 1.2235 1.88300 40.76
6 ∞ 0.0963
7 ∞ 4.2697 1.88300 40.76
8 ∞ 0
9 (Aperture) ∞ 0.4432
10 -145.9646 1.4388 1.80400 46.58
11 -3.9010 0.0963
12 ∞ 0.7707 1.49400 75.00
13 ∞ 0.2324
14 2.2305 2.4741 1.49700 81.54
15 -2.0320 0.5760 1.95906 17.47
16 -6.5656 0.9525
17 ∞ 0.6744 1.51633 64.14
18 ∞ 0.0193 1.51300 64.00
19 ∞ 0.6744 1.50510 63.26
20 ∞ 0
(Image plane) ∞

Various data IH 0.865
ω 59.893
Fno 3.148
f 1
f2 4.963
fR 2.802
fF -1.791
f3 5.951
D1 4.595
D2 1.858

Numerical Example 16
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.5925 1.88300 40.78
2 1.7485 1.2220
3 ∞ 0.7900 1.51633 64.14
4 ∞ 0.0592
5 ∞ 1.2541 1.88300 40.76
6 ∞ 0.0987
7 ∞ 4.3766 1.88300 40.76
8 ∞ 0
9 (Aperture) ∞ 0.6517
10 12.3630 1.5498 1.75500 52.32
11 -4.7631 0.0987
12 ∞ 0.7900 1.49400 75.00
13 ∞ 0.1605
14 2.3708 2.4200 1.49700 81.54
15 -2.1423 0.5907 1.95906 17.47
16 -6.2943 0.7643
17 ∞ 0.6912 1.51633 64.14
18 ∞ 0.0197 1.51300 64.00
19 ∞ 0.6912 1.50510 63.26
20 ∞ 0
(Image plane) ∞

Various data IH 0.887
ω 62.431
Fno 3.195
f 1
f2 4.739
fR 2.874
fF -1.98
f3 6.072
D1 4.891
D2 1.693

Numerical Example 17
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.5916 1.88300 40.78
2 1.7276 1.2270
3 ∞ 0.7889 1.51633 64.14
4 ∞ 0.0592
5 ∞ 1.2523 1.88300 40.76
6 ∞ 0.0986
7 ∞ 4.3702 1.88300 40.76
8 ∞ 0
9 (Aperture) ∞ 0.6508
10 39.0679 1.5518 1.78800 47.37
11 -4.3911 0.0986
12 ∞ 0.7889 1.49400 75.00
13 ∞ 0.1581
14 2.2894 2.6213 1.49700 81.54
15 -2.0170 0.5897 1.95906 17.47
16 -6.3239 0.7699
17 ∞ 0.6902 1.51633 64.14
18 ∞ 0.0197 1.51300 64.00
19 ∞ 0.6902 1.50510 63.26
20 ∞ 0
(Image plane) ∞

Various data IH 0.885
ω 62.38
Fno 3.117
f 1
f2 5.089
fR 2.875
fF -1.957
f3 6.036
D1 4.891
D2 1.697

Numerical Example 18
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.5897 1.88300 40.78
2 1.7275 1.2287
3 ∞ 0.7863 1.51633 64.14
4 ∞ 0.0590
5 ∞ 1.2483 1.88300 40.76
6 ∞ 0.0983
7 ∞ 4.3562 1.88300 40.76
8 ∞ 0
9 (Aperture) ∞ 0.6487
10 133.8224 1.6139 1.83481 42.73
11 -4.4275 0.0983
12 ∞ 0.7863 1.49400 75.00
13 ∞ 0.1672
14 2.2473 2.6028 1.49700 81.54
15 -2.0260 0.5871 1.95906 17.47
16 -6.8495 0.7971
17 ∞ 0.6880 1.51633 64.14
18 ∞ 0.0197 1.51300 64.00
19 ∞ 0.6880 1.50510 63.26
20 ∞ 0
(Image plane) ∞

Various data IH 0.883
ω 62.175
Fno 3.123
f 1
f2 5.161
fR 2.86
fF -1.956
f3 6.113
D1 4.881
D2 1.721

Numerical Example 19
Unit mm

Surface data Surface number rd nd νd
1 ∞ 0.5927 1.88300 40.78
2 1.7277 1.2468
3 ∞ 0.7902 1.49400 75.00
4 ∞ 0.0593
5 ∞ 1.2545 1.88300 40.76
6 ∞ 0.0988
7 ∞ 4.3778 1.88300 40.76
8 ∞ 0
9 (Aperture) ∞ 0.6520
10 101.7710 1.7446 1.88300 40.76
11 -4.6751 0.2923
12 2.2477 2.6232 1.49700 81.54
13 -2.0368 0.5897 1.95906 17.47
14 -8.8045 0.8458
15 ∞ 0.6914 1.51633 64.14
16 ∞ 0.0198 1.51300 64.00
17 ∞ 0.6914 1.50510 63.26
18 ∞ 0
(Image plane) ∞

Various data IH 0.887
ω 62.109
Fno 3.131
f 1
f2 5.101
fR 2.746
fF -1.957
f3 6.84
D1 4.925
D2 1.774

Next, the values of the conditional expressions in each embodiment are listed below.

Conditional expression Example 1 Example 2 Example 3 Example 4
(1) f2 / f 4.824 5.046 4.793 4.824
(2) f3 / f2 1.008 0.88 1.011 1.008
(3) fR / f 2.678 2.847 2.652 2.678
(4) fF / f -1.812 -1.863 -1.796 -1.812
(5) f3 / f 4.861 4.44 4.844 4.861
(6) D1 / f 4.168 4.198 4.062 4.168
(7) D2 / f 1.945 1.896 2.071 1.945
(8) fF / fR -0.677 -0.655 -0.677 -0.677
(9) | R3 / R2 | 0.669 0.685 0.665 0.669

Conditional expression Example 5 Example 6 Example 7 Example 8
(1) f2 / f 6.952 9.054 6.77 6.862
(2) f3 / f2 0.706 0.547 0.832 0.781
(3) fR / f 2.969 3.205 3.021 3.037
(4) fF / f -2.044 -2.464 -2.136 -2.28
(5) f3 / f 4.907 4.954 5.63 5.362
(6) D1 / f 5.325 6.517 5.763 5.926
(7) D2 / f 2.219 2.005 1.975 1.993
(8) fF / fR -0.689 -0.769 -0.707 -0.751
(9) | R3 / R2 | 0.766 0.6 0.508 0.582

Conditional expression Example 9 Example 10 Example 11 Example 12
(1) f2 / f 7.324 7.205 10.316 8.456
(2) f3 / f2 0.746 0.736 0.436 0.55
(3) fR / f 3.01 3.028 3.069 2.974
(4) fF / f -2.266 -2.272 -2.52 -2.401
(5) f3 / f 5.462 5.302 4.502 4.647
(6) D1 / f 5.876 5.955 6.69 6.332
(7) D2 / f 1.979 2.011 1.934 1.776
(8) fF / fR -0.753 -0.75 -0.821 -0.807
(9) | R3 / R2 | 0.601 0.712 0.579 0.52

Conditional expression Example 13 Example 14 Example 15 Example 16
(1) f2 / f 7.495 8.438 4.963 4.739
(2) f3 / f2 0.663 0.61 1.199 1.281
(3) fR / f 3.123 3.296 2.802 2.874
(4) fF / f -2.255 -2.432 -1.791 -1.98
(5) f3 / f 4.967 5.144 5.951 6.072
(6) D1 / f 6.257 6.984 4.595 4.891
(7) D2 / f 1.747 1.792 1.858 1.693
(8) fF / fR -0.722 -0.738 -0.639 -0.689
(9) | R3 / R2 | 0.597 0.551 0.572 0.498

Conditional expression Example 17 Example 18 Example 19
(1) f2 / f 5.089 5.161 5.101
(2) f3 / f2 1.186 1.184 1.341
(3) fR / f 2.875 2.86 2.746
(4) fF / f -1.957 -1.956 -1.957
(5) f3 / f 6.036 6.113 6.84
(6) D1 / f 4.891 4.881 4.925
(7) D2 / f 1.697 1.721 1.774
(8) fF / fR -0.68 -0.684 -0.713
(9) | R3 / R2 | 0.521 0.508 0.481

FIG. 24 is a configuration example of an endoscope device using the perspective objective optical system of the present embodiment. The endoscope device 20 includes a perspective endoscope 21 (hereinafter referred to as “endoscope 21”), a video processor 22, and a monitor 23. The endoscope 21 includes an insertion portion 21a and a signal cable 21b. A perspective objective optical system 24 is arranged at the tip of the insertion portion 21a. The perspective objective optical system 24 is, here, a perspective objective optical system for forward visual observation. As the perspective objective optical system 24, any of the perspective objective optical systems of Examples 1 to 19 is used.

Further, although not shown here, an illumination optical system for illuminating the subject 25 is arranged in the vicinity of the perspective objective optical system 24. This illumination optical system includes a light source, an illumination optical element, and an optical fiber bundle. As a light source, for example, there is a light emitting element of a light emitting diode (LED: Light Emitting Diode) or a laser diode (LD: Laser Diode). Examples of the illumination optical element include a lens element. The lens element has a function of diffusing or condensing illumination light. The optical fiber bundle transmits the illumination light to the endoscope 21.

Further, the endoscope 21 is connected to the video processor 22 via a signal cable 21b. The image of the subject 25 imaged by the perspective objective optical system 24 is imaged by the image pickup device. The image of the captured subject 25 is converted into a video signal by the electric circuit system built in the video processor 22. The image 26 of the subject is displayed on the monitor 23 based on the video signal.

Inside the video processor 22, an electric circuit system for driving a light source such as an LED is provided.

Further, by providing a light emitting element such as an LED or LD inside the endoscope 21, it is not necessary to provide a light source outside the endoscope 21. Further, by providing these light emitting elements at the tip of the endoscope 21, it is not necessary to provide an optical fiber bundle for transmitting illumination light.

Further, as the light source, a xenon lamp, a halogen lamp, or the like may be used. Further, in the endoscope device 20, a light source device having a built-in light source is integrated with the video processor 22. However, the light source device may be configured separately from the video processor 22. In this case, the light source device and the video processor 22 are connected to the endoscope 21, respectively.

As described above, according to the perspective objective optical system of the present invention, it is possible to provide a high-performance and compact perspective objective optical system that is most suitable for an image pickup device having a large number of pixels and a small size. Further, by using the perspective objective optical system of the present invention, it is possible to obtain a high-quality image and provide a perspective endoscope having a reduced diameter tip portion.

Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and the embodiments are configured by appropriately combining the configurations of these embodiments without departing from the spirit of the present invention. The form is also within the scope of the present invention.

(Additional note)
The inventions having the following configurations are derived from these examples.
(Appendix 1)
From the object side, it consists of a front lens group having a negative refractive power, an optical path conversion element, a brightness aperture, and a posterior lens group having a positive refractive power.
The front lens group consists of front negative lenses.
The rear lens group consists of a rear positive lens and a junction lens having a positive refractive power.
A perspective objective optical system characterized by satisfying the following conditional expression (1).
4.0 <f2 / f <12.0 (1)
here,
f2 is the focal length of the rear positive lens,
f is the focal length of the entire perspective objective optical system,
Is.

(Appendix 2)
The perspective objective optical system according to Appendix 1, which satisfies the following conditional expression (2).
0.4 <f3 / f2 <1.5 (2)
here,
f2 is the focal length of the rear positive lens,
f3 is the focal length of the junction lens,
Is.

(Appendix 3)
The perspective objective optical system according to Supplementary Item 1 or Supplementary Item 2, characterized in that the following conditional expression (3) is satisfied.
2.3 <fR / f <3.8 (3)
here,
fR is the focal length of the rear lens group,
f is the focal length of the entire perspective objective optical system,
Is.

(Appendix 4)
The perspective objective optical system according to any one of Supplementary Items 1 to 3, wherein the perspective objective optical system is characterized by satisfying the following conditional expression (4).
-2.8 <fF / f <-1.5 (4)
here,
fF is the focal length of the front lens group,
f is the focal length of the entire perspective objective optical system,
Is.

(Appendix 5)
The perspective objective optical system according to any one of Supplementary Items 1 to 4, wherein the perspective objective optical system is characterized by satisfying the following conditional expression (5).
4.0 <f3 / f <8.0 (5)
here,
f3 is the focal length of the junction lens,
f is the focal length of the entire perspective objective optical system,
Is.

(Appendix 6)
The perspective objective optical system according to any one of Supplementary Items 1 to 5, characterized in that the following conditional expression (6) is satisfied.
3.5 <D1 / f <8.0 (6)
here,
D1 is the air equivalent length from the image side of the front negative lens to the brightness aperture.
f is the focal length of the entire perspective objective optical system,
Is.

(Appendix 7)
The perspective objective optical system according to any one of Supplementary Items 1 to 6, wherein the perspective objective optical system is characterized by satisfying the following conditional expression (7).
1.5 <D2 / f <2.5 (7)
here,
D2 is the air equivalent length from the image side to the image plane of the final lens of the rear lens group.
f is the focal length of the entire perspective objective optical system,
Is.

(Appendix 8)
The perspective objective optical system according to any one of Supplementary Items 1 to 7, wherein the perspective objective optical system is characterized by satisfying the following conditional expression (8).
-0.9 <fF / fR <-0.5 (8)
here,
fF is the focal length of the front lens group,
fR is the focal length of the rear lens group,
Is.

(Appendix 9)
The rear positive lens faces the surface with a small radius of curvature toward the image side.
The bonded lens faces the surface with a small radius of curvature toward the object.
The perspective objective optical system according to any one of Supplementary Items 1 to 8, wherein the perspective objective optical system is characterized by satisfying the following conditional expression (9).
0.4 << R3 / R2 | <0.85 (9)
here,
R2 is the radius of curvature of the image side of the rear positive lens,
R3 is the radius of curvature of the side surface of the object of the bonded lens,
Is.

(Appendix 10)
A perspective endoscope comprising the perspective objective optical system according to any one of Supplementary Items 1 to 9.

As described above, the present invention is useful for high-performance and compact perspective objective optical systems. In addition, a high-quality image can be obtained, and it is useful for a squint endoscope having a reduced-diameter tip portion.

GF Front lens group GR Rear lens group L1, L2, L3, L4 Lens CL Bonded lens S Brightness diaphragm P prism (optical path conversion element)
F1, F2, F3 filter CG cover glass GL glass lid I image plane ID image pickup element 1, 5 perspective objective optical system 2, 6 front lens group 3, 7 prism 4, 8 rear lens group 20 endoscope device 21 for perspective Endoscope 21a Insertion part 21b Signal cable 22 Video processor 23 Monitor 24 Perspective objective optical system 25 Subject 26 Subject image

Claims (2)

From the object side, it consists of a front lens group having a negative refractive power, an optical path conversion element, a brightness aperture, and a posterior lens group having a positive refractive power.
The front lens group consists of a front negative lens.
The rear lens group includes a rear positive lens and a junction lens having a positive refractive power.
A perspective objective optical system characterized by satisfying the following conditional expressions (1) and ( 3').
4.0 <f2 / f <12.0 (1)
2.652 ≤ fR / f <3.8 (3')
However,
f2 is the focal length of the rear positive lens,
f is the focal length of the entire perspective objective optical system,
fR is the focal length of the rear lens group,
Is. A perspective endoscope comprising the perspective objective optical system according to claim 1.

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