JP2020112776A - Endoscope objective lens and endoscope - Google Patents

Abstract

To provide an endoscope objective lens which is well corrected for both chromatic aberration and distortion aberration and offers high optical performance, and to provide an endoscope having the same.SOLUTION: An endoscope objective lens provided herein consists of, in order from the object side, a first lens group consisting of a negative lens, a second lens group consisting of a negative lens, a third lens group consisting of a cemented lens, an aperture stop, a fourth lens group consisting of a single lens having positive refractive power or a cemented lens having positive refractive power as a whole, and a fifth lens group consisting of a cemented lens comprised of two lenses with refractive power of opposite signs cemented together, and is configured to satisfy a predefined conditional expression regarding the cemented lenses.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an objective lens for an endoscope and an endoscope.

2. Description of the Related Art Conventionally, an endoscope has been used in the medical field for observing and treating a patient's body. The following Patent Documents 1 and 2 describe a lens system that can be used as an objective lens for an endoscope. These lens systems include, in order from the object side to the image side, a group having negative refractive power and a group having positive refractive power.

Japanese Patent No. 6161520 JP, 2017-26802, A

In recent years, an image captured by an endoscope is subjected to image processing to generate an image in which a surface structure or the like is emphasized, and a lesion is highlighted and observed. In such an observation, in addition to a white light source, a laser light source with a short wavelength around 400 nm (nanometer) may be used as a light source. In that case, an endoscope objective lens in which chromatic aberration is satisfactorily corrected in the entire region from the short wavelength region to the visible region is required. On the other hand, in endoscopic observation accompanied by surgical treatment, it is required that the image has little distortion in order to specify the treatment range and perform accurate treatment. Therefore, the distortion aberration is corrected well. Objective lenses for endoscopes are required. From the above, it is desired that both the chromatic aberration and the distortion are well-balanced and well corrected in the endoscope objective lens.

However, the lens system described in Patent Document 1 cannot be said to be one in which both chromatic aberration and distortion are sufficiently corrected. The lens system described in Patent Document 2 has room for improvement in terms of maintaining a good balance between correction of distortion and correction of lateral chromatic aberration.

The present disclosure has been made in view of the above circumstances, and is provided with an endoscope objective lens having high optical performance, in which both chromatic aberration and distortion are favorably corrected, and the endoscope objective lens. It is intended to provide an endoscope.

An endoscope objective lens according to an aspect of the present disclosure includes, in order from an object side to an image side, a first lens group including a negative lens, a second lens group including a negative lens, and two lenses. A third lens group consisting of cemented cemented lenses, an aperture stop, and a single lens having positive refracting power or two lenses cemented together to form a fourth cemented lens having a positive refracting power as a whole. The fifth lens group includes a lens group and a cemented lens in which two lenses having refractive powers of opposite signs are cemented, and the total number of cemented lenses is k, a natural number from 1 to k is i, and the object is The d-line-based Abbe number of the object-side lens that forms the i-th cemented lens from the side is νai, and the d-line-based Abbe number of the image-side lens that forms the i-th cemented lens from the object side is νbi. When the distance from the stop to the cemented surface of the i-th cemented lens on the optical axis is Dci and the radius of curvature of the cemented surface of the i-th cemented lens from the object side is Rci, the following conditional expression (1) is given. To be satisfied.

It is preferable that the endoscope objective lens of the above aspect satisfies the following conditional expression (1-1).

In the objective lens for an endoscope of the above aspect, the combined focal length of the first lens group and the second lens group is f12, the focal length of the third lens group is f3, and the image side surface of the negative lens of the first lens group. Rr1, the radius of curvature of the object side surface of the negative lens of the first lens group is Rf1, the radius of curvature of the image side surface of the negative lens of the second lens group is Rr2, and the negative lens of the second lens group is When the curvature radius of the surface on the object side is Rf2, it is preferable that the following conditional expression (2) is satisfied, and it is more preferable that the following conditional expression (2-1) is satisfied.

The endoscope objective lens of the above aspect satisfies the following conditional expression (3), where Rr3 is the radius of curvature of the image-side surface of the third lens group and f is the focal length of the endoscope objective lens. It is more preferable to satisfy the following conditional expression (3-1).
-20<Rr3/f<-0.5 (3)
-12<Rr3/f<-1 (3-1)

The endoscope objective lens of the above aspect satisfies the following conditional expression (4), where Rr4 is the radius of curvature of the image-side surface of the fourth lens group and f is the focal length of the endoscope objective lens. It is more preferable to satisfy the following conditional expression (4-1).
-2.5<Rr4/f<-1 (4)
-2.2<Rr4/f<-1.2 (4-1)

In the objective lens for an endoscope of the above aspect, when the radius of curvature of the most image-side surface of the fifth lens group is Rr5 and the radius of curvature of the most object-side surface of the fifth lens group is Rf5, the following conditional expression ( It is preferable to satisfy 5), and it is more preferable to satisfy the following conditional expression (5-1).
-0.5<(Rr5+Rf5)/(Rr5-Rf5)<1 (5)
-0.25<(Rr5+Rf5)/(Rr5-Rf5)<0.7 (5-1)

In the objective lens for an endoscope of the above aspect, the distance on the optical axis from the aperture stop to the lens surface closest to the object is Df, and the distance on the optical axis from the aperture stop to the lens surface closest to the image is Dr. In this case, it is preferable to satisfy the following conditional expression (6), and it is more preferable to satisfy the following conditional expression (6-1).
0.5<Df/Dr<1.5 (6)
0.8<Df/Dr<1.2 (6-1)

In the endoscope objective lens of the above aspect, the combined focal length of the first lens group, the second lens group, and the third lens group is f123, and the combined focal length of the fourth lens group and the fifth lens group is f45. In this case, it is preferable to satisfy the following conditional expression (7), and it is more preferable to satisfy the following conditional expression (7-1).
1.5<|f123/f45|<10 (7)
1.8<|f123/f45|<8 (7-1)

An endoscope according to another aspect of the present disclosure includes the endoscope objective lens according to the above aspect of the present disclosure.

In addition, "consisting of" and "consisting of" in the present specification mean, in addition to the listed components, a lens having substantially no refractive power, and a lens such as a diaphragm, a filter, and a cover glass. It is intended that optical elements other than the above, and a lens flange, a lens barrel, an imaging element, and the like may be included.

The “group having a positive refractive power” in the present specification means that the group as a whole has a positive refractive power. Similarly, “having negative refractive power-group” means having negative refractive power as a whole. "Lens having positive refractive power", "positive lens", and "positive lens" are synonymous. "Lens having negative refractive power", "negative lens", and "negative lens" are synonymous.

"Single lens" means a single lens that is not cemented. A compound aspherical lens (a lens in which a spherical lens and an aspherical film formed on the spherical lens are integrally configured to function as one aspherical lens as a whole) is regarded as a cemented lens. No, treat it as one lens. The sign of the refractive power, the radius of curvature of the lens surface, and the surface shape of the lens surface regarding a lens including an aspherical surface will be considered in the paraxial region unless otherwise specified. Regarding the sign of the radius of curvature, the sign of the radius of curvature of the surface having the convex surface facing the object side is positive, and the sign of the radius of curvature of the surface having the convex surface facing the image side is negative.

In the present specification, the “focal length” used in the conditional expression is a paraxial focal length. The values used in the conditional expressions are the values when the d line is used as a reference. The "d line", "C line", and "F line" described in this specification are bright lines, the wavelength of the d line is 587.56 nm (nanometers), and the wavelength of the C line is 656.27 nm (nanometers). ), and the wavelength of the F line is 486.13 nm (nanometer). In this specification, “in order from the object side” regarding the arrangement order is synonymous with “in order from the object side to the image side”.

According to the present disclosure, it is possible to provide an endoscope objective lens having high optical performance in which both chromatic aberration and distortion are satisfactorily corrected, and an endoscope including the endoscope objective lens. it can.

FIG. 3 is a cross-sectional view showing a configuration of an endoscope objective lens according to an embodiment of the present disclosure. FIG. 3 is a cross-sectional view showing a configuration and a light flux of an endoscope objective lens of Example 1 of the present disclosure. FIG. 6 is a cross-sectional view showing a configuration and a light flux of an endoscope objective lens of Example 2 of the present disclosure. FIG. 5 is a cross-sectional view showing a configuration and a light flux of an endoscope objective lens of Example 3 of the present disclosure. FIG. 8 is a cross-sectional view showing a configuration and a light flux of an endoscope objective lens of Example 4 of the present disclosure. FIG. 9 is a cross-sectional view showing a configuration and a light flux of an endoscope objective lens of Example 5 of the present disclosure. FIG. 8 is a cross-sectional view showing a configuration and a light flux of an endoscope objective lens of Example 6 of the present disclosure. FIG. 9 is a cross-sectional view showing a configuration and a light flux of an endoscope objective lens of Example 7 of the present disclosure. FIG. 13 is a cross-sectional view showing a configuration and a light flux of an endoscope objective lens of Example 8 of the present disclosure. FIG. 4 is a diagram illustrating each aberration of the endoscope objective lens according to the first embodiment of the present disclosure. FIG. 7 is a diagram illustrating each aberration of the endoscope objective lens according to the second embodiment of the present disclosure. FIG. 9 is a diagram illustrating each aberration of the endoscope objective lens according to the third embodiment of the present disclosure. FIG. 8 is a diagram illustrating each aberration of the endoscope objective lens according to the fourth embodiment of the present disclosure. FIG. 10 is a diagram of aberrations of the endoscope objective lens according to the fifth embodiment of the present disclosure. FIG. 13 is a diagram of each aberration of the endoscope objective lens according to the sixth embodiment of the present disclosure. FIG. 13 is a diagram of aberrations of the endoscope objective lens of Example 7 of the present disclosure. FIG. 16 is a diagram of aberrations of the endoscope objective lens of Example 8 of the present disclosure. 1 is a schematic configuration diagram of an endoscope according to an embodiment of the present disclosure.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing the configuration of an endoscope objective lens 1 according to an embodiment of the present disclosure. The example shown in FIG. 1 corresponds to Example 1 described later. In FIG. 1, the left side is the object side and the right side is the image side.

Note that, in FIG. 1, an example in which a cover glass CG is arranged on the object side of the endoscope objective lens 1 and an optical member PP is arranged on the image side of the endoscope objective lens 1 in consideration of usage conditions. Is shown. The optical member PP is a member assuming various filters and/or prisms. The various filters are, for example, a low pass filter, an infrared cut filter, a filter that cuts a specific wavelength range, and the like. The cover glass CG and the optical member PP are members that do not have a refractive power in which the entrance surface and the exit surface are parallel and are not lenses. In the present disclosure, a configuration in which at least one of the cover glass CG and the optical member PP is omitted is also possible. Although FIG. 1 shows an example in which the image plane Sim is located on the image side surface of the optical member PP, the position of the image plane Sim is not limited to this position in the present disclosure. It should be noted that the image plane Sim shown in FIG. 1 does not show the size but shows the position on the optical axis.

The endoscope objective lens 1 of the present disclosure includes a first lens group G1, a second lens group G2, a third lens group G3, and an aperture in order from the object side to the image side along the optical axis Z. The diaphragm St includes a fourth lens group G4 and a fifth lens group G5. The first lens group G1 is composed of one negative lens. The second lens group G2 is composed of one negative lens. The third lens group G3 is composed of a cemented lens configured by cementing two lenses. The fourth lens group G4 is composed of one single lens having a positive refracting power, or a cemented lens having a positive refracting power as a whole formed by cementing two lenses. That is, the fourth lens group G4 is composed of one lens component having a positive refractive power. The “lens component” is a lens having only two air-contact surfaces on the optical axis, the surface on the object side and the surface on the image side, and one lens component means one single lens or one cemented lens. Means a lens. The fifth lens group G5 is composed of a cemented lens configured by cementing two lenses having refractive powers of opposite signs. The cemented lens including two lenses having refractive powers having opposite signs may be a cemented lens in which a positive lens and a negative lens are cemented in order from the object side, and the negative lens and the positive lens are sequentially arranged from the object side. It may be a cemented lens that is cemented.

By configuring the first lens group G1 and the second lens group G2 as described above, and disposing two negative lenses consecutively in order from the most object side, distortion can be maintained while maintaining a wide angle of view. It is advantageous to suppress it.

The third lens group G3 is advantageous in miniaturization because it is configured by cementing two lenses. When the third lens group G3 is composed of two lenses having refractive powers of opposite signs, it is advantageous for correction of lateral chromatic aberration. When the third lens group G3 is composed of two positive lenses, it is advantageous in correcting distortion.

By arranging the aperture stop St at approximately the center of the lens system as described above, a lens system having good symmetry with respect to the aperture stop St can be configured, which is advantageous for suppressing distortion. The aperture stop St shown in FIG. 1 does not show a shape but a position on the optical axis.

In the lens system in which the first lens group G1 and the second lens group G2 have negative refracting power, the fourth lens group G4 having the above configuration can suppress the generation of astigmatism and field curvature. When the fourth lens group G4 is composed of one single lens, it is advantageous for downsizing. When the fourth lens group G4 is composed of a cemented lens configured by cementing two lenses having refractive powers of opposite signs to each other, it is advantageous for correction of chromatic aberration.

The fifth lens group G5 is a lens group far from the aperture stop St and closest to the image plane Sim. By configuring the fifth lens group G5 as described above, it is advantageous for correction of lateral chromatic aberration.

As an example, in the endoscope objective lens 1 shown in FIG. 1, the first lens group G1 is made up of one lens L1 and the second lens group G2 is made up of one lens L2. The lens group G3 is composed of two lenses L31 to L32 in order from the object side to the image side, and the fourth lens group G4 is composed of two lenses L41 to L42 in order from the object side to the image side. The fifth lens group G5 is composed of two lenses L51 to L52 in order from the object side to the image side.

The total number of cemented lenses that the objective lens 1 for an endoscope has is k, a natural number from 1 to k is i, the Abbe number of the lens on the object side that constitutes the i-th cemented lens from the object side is νai based on the d-line, The d-line-based Abbe number of the image-side lens forming the i-th cemented lens from the object side is νbi, and the distance on the optical axis from the object side to the cemented surface of the i-th cemented lens is Dci. When the radius of curvature of the cemented surface of the i-th cemented lens from the object side is Rci, the endoscope objective lens 1 is configured to satisfy the following conditional expression (1). If the lower limit of conditional expression (1) is not exceeded, it becomes easy to correct axial chromatic aberration and lateral chromatic aberration that occur in the first lens group G1 and the second lens group G2. Further, the objective lens 1 for an endoscope preferably satisfies the following conditional expression (1-1). By setting the conditional expression (1-1) so as not to fall below the lower limit, it becomes easier to correct axial chromatic aberration and lateral chromatic aberration that occur in the first lens group G1 and the second lens group G2. By setting the conditional expression (1-1) so as not to exceed the upper limit, it is advantageous for downsizing the lens system in the optical axis direction.

In the example shown in FIG. 1, the total number of cemented lenses included in the endoscope objective lens 1 is three. As an example, FIG. 1 shows Dc1, Dc2, and Dc3 as the distances on the optical axis between the cemented surfaces of the first, second, and third cemented lenses from the object side and the aperture stop St, respectively, from the object side. Rc1, Rc2, and Rc3 are shown as the radii of curvature of the cemented surfaces of the first, second, and third cemented lenses, respectively.

The combined focal length of the first lens group G1 and the second lens group G2 is f12, the focal length of the third lens group G3 is f3, the radius of curvature of the image side surface of the negative lens of the first lens group G1 is Rr1, and The radius of curvature of the object side surface of the negative lens of the first lens group G1 is Rf1, the radius of curvature of the image side surface of the negative lens of the second lens group G2 is Rr2, and the object side surface of the negative lens of the second lens group G2. When the radius of curvature of Rf2 is Rf2, it is preferable that the endoscope objective lens 1 satisfies the following conditional expression (2). In the conditional expression (2), (Rr1+Rf1)/(Rr1-Rf1) and (Rr2+Rf2)/(Rr2-Rf2) are terms relating to the lens shape of the first lens group G1 and the lens shape of the second lens group G2, respectively. By not falling below the lower limit of conditional expression (2), it becomes easy to maintain a wide angle of view suitable as an objective optical system for an endoscope. By setting the conditional expression (2) so as not to exceed the upper limit, it becomes easy to appropriately control the refraction of off-axis rays and suppress distortion. If the constitution satisfies the following conditional expression (2-1), better characteristics can be obtained.

When the radius of curvature of the most image-side surface of the third lens group G3 is Rr3 and the focal length of the endoscope objective lens 1 is f, the endoscope objective lens 1 satisfies the following conditional expression (3). It is preferable. If the lower limit of conditional expression (3) is not exceeded, the positive refractive power of the most image-side surface of the third lens group G3 can be ensured, which is advantageous for downsizing. If the upper limit of conditional expression (3) is not exceeded, the positive refracting power of the most image-side surface of the third lens group G3 will not be excessive, and thus field curvature and astigmatism will be excellent. Can contribute to the correction. If the constitution satisfies the following conditional expression (3-1), better characteristics can be obtained.
-20<Rr3/f<-0.5 (3)
-12<Rr3/f<-1 (3-1)

When the radius of curvature of the most image-side surface of the fourth lens group G4 is Rr4 and the focal length of the endoscope objective lens 1 is f, the endoscope objective lens 1 satisfies the following conditional expression (4). It is preferable. By not falling below the lower limit of conditional expression (4), the positive refractive power of the most image-side surface of the fourth lens group G4 can be secured, which is advantageous for downsizing. By ensuring that the upper limit of conditional expression (4) is not exceeded, the positive refractive power of the most image-side surface of the fourth lens group G4 does not become excessive, which contributes to good correction of distortion. You can Note that better characteristics can be obtained if the configuration satisfies the following conditional expression (4-1).
-2.5<Rr4/f<-1 (4)
-2.2<Rr4/f<-1.2 (4-1)

When the radius of curvature of the most image-side surface of the fifth lens group G5 is Rr5 and the radius of curvature of the most object-side surface of the fifth lens group G5 is Rf5, the endoscope objective lens 1 has the following conditional expression (5). ) Is preferably satisfied. It is advantageous for correction of the distortion aberration that the lower limit of conditional expression (5) is not exceeded. Not exceeding the upper limit of the conditional expression (5) is advantageous for correction of field curvature, and also advantageous for reducing the incident angle of the principal ray of the off-axis light beam on the image plane Sim. It should be noted that if the constitution satisfies the following conditional expression (5-1), it is possible to obtain better characteristics.
-0.5<(Rr5+Rf5)/(Rr5-Rf5)<1 (5)
-0.25<(Rr5+Rf5)/(Rr5-Rf5)<0.7 (5-1)

When the distance on the optical axis from the aperture stop St to the lens surface closest to the object is Df and the distance on the optical axis from the aperture stop St to the lens surface closest to the image is Dr, the objective lens 1 for endoscope 1 Preferably satisfies the following conditional expression (6). As an example, FIG. 1 shows Df and Dr in the objective lens 1 for an endoscope. By not falling below the lower limit of conditional expression (6), it is easy to suppress distortion while maintaining the balance between the length of the object-side lens system of the aperture stop St and the length of the image-side lens system. Becomes If the upper limit of conditional expression (6) is not exceeded, it is advantageous for reducing the diameter of the lens closest to the object side. If the constitution satisfies the following conditional expression (6-1), better characteristics can be obtained.
0.5<Df/Dr<1.5 (6)
0.8<Df/Dr<1.2 (6-1)

When the combined focal length of the first lens group G1, the second lens group G2, and the third lens group G3 is f123 and the combined focal length of the fourth lens group G4 and the fifth lens group G5 is f45, the endoscope The objective lens 1 for use preferably satisfies the following conditional expression (7). Conditional expression (7) is an expression regarding the ratio between the combined refractive power of all the lens groups on the object side of the aperture stop St and the combined refractive power of all the lens groups on the image side of the aperture stop St. It is advantageous to correct the distortion aberration favorably while maintaining the wide angle of view by setting the conditional expression (7) so as not to fall below the lower limit. By making the upper limit of conditional expression (7) not exceeded, the diameter of the lens closest to the object side can be reduced while balancing the refractive power of the object-side lens and the image-side lens of the aperture stop St. It becomes easy to plan. If the constitution satisfies the following conditional expression (7-1), better characteristics can be obtained.
1.5<|f123/f45|<10 (7)
1.8<|f123/f45|<8 (7-1)

The above-described preferable configurations and/or possible configurations, including the configurations related to the conditional expressions, can be arbitrarily combined, and are preferably selectively adopted in accordance with required specifications. According to the endoscope objective lens 1 of the present disclosure, both chromatic aberration and distortion are favorably corrected, and high optical performance can be realized.

Next, numerical examples of the endoscope objective lens of the present disclosure will be described. In addition, all the data of the examples shown below are data in the case where the focal length of the endoscope objective lens is standardized to be 1.
[Example 1]
FIG. 2 is a cross-sectional view showing the structure and light flux of the endoscope objective lens of the first embodiment. FIG. 2 shows, as the luminous flux, an axial luminous flux 2 and a luminous flux 3 having a maximum angle of view. Further, FIG. 2 also shows the cover glass CG and the optical member PP as in FIG. 1 in consideration of the usage situation. The endoscope objective lens of Example 1 has, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and a positive lens group G2. It includes a third lens group G3 having a refractive power, an aperture stop St, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. The aperture stop St shown in FIG. 2 does not show a shape but a position on the optical axis. The first lens group G1 is composed of a negative lens L1. The second lens group G2 is composed of a negative lens L2. The third lens group G3 is composed of a cemented lens in which a positive lens L31 and a positive lens L32 are cemented in order from the object side. The fourth lens group G4 is composed of a cemented lens in which a negative lens L41 and a positive lens L42 are cemented in order from the object side. The fifth lens group G5 is composed of a cemented lens in which a positive lens L51 and a negative lens L52 are cemented in order from the object side.

Table 1 shows the basic lens data and Table 2 shows the specifications of the endoscope objective lens of Example 1. In Table 1, in the column of Sn, the surface number in the case where the surface closest to the object side is the first surface and the number is increased by 1 toward the image side is shown, and in the column of R, the radius of curvature of each surface is shown. In the column of D, the surface spacing on the optical axis between each surface and the surface adjacent to the image side is shown. The Nd column shows the refractive index of each component with respect to the d-line, and the νd column shows the Abbe number of each component with respect to the d-line.

In Table 1, the sign of the curvature radius of the surface having the convex surface facing the object side is positive, and the sign of the curvature radius of the surface having the convex surface facing the image side is negative. Table 1 also shows the cover glass CG, the aperture diaphragm St, and the optical member PP, and the surface number and the phrase (St) are described in the field of the surface number of the surface corresponding to the aperture diaphragm St. The value in the bottom column of D in Table 1 is the distance between the most image-side surface and the image surface Sim in the table.

Table 2 shows the focal length f of the endoscope objective lens, the back focus Bf at the air conversion distance, the F number FNo. , And the value of the maximum total angle of view 2ω are shown on the d-line basis. (°) in the column of 2ω means that the unit is degrees. Tables 1 and 2 show numerical values rounded to a predetermined digit.

FIG. 10 shows aberration diagrams of the endoscope objective lens of the first example. In FIG. 10, spherical aberration, astigmatism, distortion, and lateral chromatic aberration are shown in order from the left. In the spherical aberration diagram, aberrations at d line, C line, and F line are shown by a solid line, a long broken line, and a short broken line, respectively. In the astigmatism diagram, the aberration at the d-line in the sagittal direction is shown by a solid line, and the aberration at the d-line in the tangential direction is shown by a short broken line. In the distortion diagram, the solid line shows the aberration at the d-line. In the lateral chromatic aberration diagram, the aberrations at the C line and the F line are indicated by a long broken line and a short broken line, respectively. FNo. Means an F number, and ω in other aberration diagrams means a half angle of view. The data shown in Table 1 and FIG. 10 are data when the distance from the object to the object-side surface of the cover glass CG is 21.

The symbols, meanings, description methods, and illustration methods of the respective data relating to the above-described first embodiment are the same in the following embodiments unless otherwise specified, and thus duplicated description will be omitted below.

[Example 2]
FIG. 3 is a cross-sectional view showing the structure and light flux of the endoscope objective lens of the second embodiment. The endoscope objective lens of Example 2 has, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and a positive lens group G2. It includes a third lens group G3 having a refractive power, an aperture stop St, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. The first lens group G1 is composed of a negative lens L1. The second lens group G2 is composed of a negative lens L2. The third lens group G3 is composed of a cemented lens in which a positive lens L31 and a negative lens L32 are cemented in order from the object side. The fourth lens group G4 is composed of a cemented lens in which a positive lens L41 and a positive lens L42 are cemented in order from the object side. The fifth lens group G5 is composed of a cemented lens in which a positive lens L51 and a negative lens L52 are cemented in order from the object side.

Regarding the objective lens for an endoscope of Example 2, basic lens data is shown in Table 3, specifications are shown in Table 4, and aberration diagrams are shown in FIG. 11. These data are data when the distance from the object to the object-side surface of the cover glass CG is 25.

[Example 3]
FIG. 4 is a sectional view showing the structure and luminous flux of the endoscope objective lens of the third embodiment. The endoscope objective lens of Example 3 has, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and a positive lens group G2. It includes a third lens group G3 having a refractive power, an aperture stop St, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. The first lens group G1 is composed of a negative lens L1. The second lens group G2 is composed of a negative lens L2. The third lens group G3 is composed of a cemented lens in which a positive lens L31 and a negative lens L32 are cemented in order from the object side. The fourth lens group G4 is composed of a cemented lens in which a negative lens L41 and a positive lens L42 are cemented in order from the object side. The fifth lens group G5 is composed of a cemented lens in which a positive lens L51 and a negative lens L52 are cemented in order from the object side.

Table 5 shows basic lens data, Table 6 shows specifications, and FIG. 12 shows aberration diagrams of the objective lens for an endoscope of Example 3. These data are data when the distance from the object to the object-side surface of the cover glass CG is 22.

[Example 4]
FIG. 5 is a sectional view showing the structure of the objective lens for an endoscope of Example 4 and the luminous flux. The endoscope objective lens of Example 4 has, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and a positive lens group G2. It includes a third lens group G3 having a refractive power, an aperture stop St, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. The first lens group G1 is composed of a negative lens L1. The second lens group G2 is composed of a negative lens L2. The third lens group G3 is composed of a cemented lens in which a negative lens L31 and a positive lens L32 are cemented in order from the object side. The fourth lens group G4 is composed of a cemented lens in which a negative lens L41 and a positive lens L42 are cemented in order from the object side. The fifth lens group G5 is composed of a cemented lens in which a positive lens L51 and a negative lens L52 are cemented in order from the object side.

Table 7 shows basic lens data, Table 8 shows specifications, and FIG. 13 shows aberration diagrams of the objective lens for an endoscope of Example 4. These data are data when the distance from the object to the object-side surface of the cover glass CG is 23.

[Example 5]
FIG. 6 is a sectional view showing the structure of the objective lens for an endoscope of Example 5 and the luminous flux. The endoscope objective lens of Example 5 has, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and a positive lens group G2. It includes a third lens group G3 having a refractive power, an aperture stop St, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. The first lens group G1 is composed of a negative lens L1. The second lens group G2 is composed of a negative lens L2. The third lens group G3 is composed of a cemented lens in which a positive lens L31 and a negative lens L32 are cemented in order from the object side. The fourth lens group G4 is composed of a positive lens L4. The fifth lens group G5 is composed of a cemented lens in which a positive lens L51 and a negative lens L52 are cemented in order from the object side.

For the endoscope objective lens of Example 5, basic lens data is shown in Table 9, specifications are shown in Table 10, and aberration diagrams are shown in FIG. 14. These data are data when the distance from the object to the object-side surface of the cover glass CG is 23.

[Example 6]
FIG. 7 is a cross-sectional view showing the structure and light flux of the endoscope objective lens of the sixth embodiment. The endoscope objective lens of Example 6 has, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and a positive lens group G2. It includes a third lens group G3 having a refractive power, an aperture stop St, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. The first lens group G1 is composed of a negative lens L1. The second lens group G2 is composed of a negative lens L2. The third lens group G3 is composed of a cemented lens in which a positive lens L31 and a negative lens L32 are cemented in order from the object side. The fourth lens group G4 is composed of a positive lens L4. The fifth lens group G5 is composed of a cemented lens in which a positive lens L51 and a negative lens L52 are cemented in order from the object side.

Table 11 shows basic lens data, Table 12 shows specifications, and FIG. 15 shows aberration diagrams of the objective lens for an endoscope of Example 6. These data are data when the distance from the object to the object-side surface of the cover glass CG is 22.

[Example 7]
FIG. 8 is a sectional view showing the structure of the objective lens for an endoscope of Example 7 and the luminous flux. The endoscope objective lens of Example 7 has, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and a positive lens group G2. It includes a third lens group G3 having a refractive power, an aperture stop St, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. The first lens group G1 is composed of a negative lens L1. The second lens group G2 is composed of a negative lens L2. The third lens group G3 is composed of a cemented lens in which a positive lens L31 and a negative lens L32 are cemented in order from the object side. The fourth lens group G4 is composed of a positive lens L4. The fifth lens group G5 is composed of a cemented lens in which a positive lens L51 and a negative lens L52 are cemented in order from the object side.

Table 13 shows basic lens data, Table 14 shows specifications, and FIG. 16 shows aberration diagrams of the objective lens for an endoscope of Example 7. These data are data when the distance from the object to the object-side surface of the cover glass CG is 26.

[Example 8]
FIG. 9 is a sectional view showing the structure of the objective lens for an endoscope of Example 8 and the luminous flux. The endoscope objective lens of Example 8 has a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and a positive lens group in order from the object side to the image side. It includes a third lens group G3 having a refractive power, an aperture stop St, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. The first lens group G1 is composed of a negative lens L1. The second lens group G2 is composed of a negative lens L2. The third lens group G3 is composed of a cemented lens in which a positive lens L31 and a negative lens L32 are cemented in order from the object side. The fourth lens group G4 is composed of a positive lens L4. The fifth lens group G5 is composed of a cemented lens in which a negative lens L51 and a positive lens L52 are cemented in order from the object side.

Table 15 shows basic lens data, Table 16 shows specifications, and FIG. 17 shows aberration diagrams of the objective lens for an endoscope of Example 8. These data are data when the distance from the object to the object-side surface of the cover glass CG is 22.

Table 17 shows corresponding values of the conditional expressions (1) to (7) of the endoscope objective lenses of Examples 1 to 8. Examples 1 to 8 use the d line as the reference wavelength. Table 17 shows the values based on the d-line.

As can be seen from the above data, the endoscope objective lenses of Examples 1 to 8 are small in size, various aberrations including chromatic aberration and distortion are well corrected, and high optical performance is realized. ..

Next, the endoscope according to the embodiment of the present disclosure will be described. FIG. 18 shows a schematic overall configuration diagram of an endoscope according to an embodiment of the present disclosure. The endoscope 100 shown in FIG. 18 mainly includes an operation unit 102, an insertion unit 104, and a universal cord 106 connected to a connector unit (not shown). Most of the insertion portion 104 is a flexible portion 107 that bends in an arbitrary direction along the insertion path. A bending portion 108 is connected to the tip of the flexible portion 107, and a tip portion 110 is connected to the tip of the bending portion 108. There is. The bending portion 108 is provided to orient the tip portion 110 in a desired direction, and the bending operation can be performed by rotating the bending operation knob 109 provided on the operation portion 102. The endoscope objective lens 1 according to the embodiment of the present disclosure is disposed at the inner tip of the tip portion 110. In FIG. 18, the endoscope objective lens 1 is schematically illustrated. Since the endoscope of the present disclosure includes the endoscope objective lens according to the embodiment of the present disclosure, a good image can be acquired.

Although the technology of the present disclosure has been described above with reference to the embodiments and examples, the technology of the present disclosure is not limited to the above-described embodiments and examples, and various modifications are possible. For example, the radius of curvature, surface spacing, refractive index, Abbe number, etc. of each lens are not limited to the values shown in the above-mentioned numerical examples, and can take other values.

1 Objective Lens for Endoscope 2 Luminous Flux on Axis 3 Luminous Flux 100 at Maximum Angle of View 100 Endoscope 102 Operation Part 104 Insertion Part 106 Universal Code 107 Flexible Part 108 Bending Part 109 Bending Operation Knob 110 Tip CG Cover Glass Df From Aperture Stop Distance on the optical axis to the lens surface closest to the object side Dr. Distance on the optical axis from the aperture stop to the lens surface closest to the image side G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group G5 Fifth lens group L1, L2, L31, L32, L4, L41, L42, L51, L52 Lens PP Optical members Rc1, Rc2, Rc3 Radius of curvature Dc1, Dc2, Dc3 of the cemented surface Optical axis from the aperture stop to the cemented surface Upper distance Sim Image plane St Aperture stop Z Optical axis

Claims (15)

In order from the object side to the image side, a first lens group including a negative lens, a second lens group including a negative lens, a third lens group including a cemented lens formed by cementing two lenses, and an aperture. A stop, a fourth lens group including a cemented lens having a positive refracting power as a whole by cementing a single lens having a positive refracting power or two lenses, and two lenses having a refracting power having mutually different signs. A fifth lens group consisting of a cemented lens in which lenses are cemented,
The total number of cemented lenses is k,
I is a natural number from 1 to k,
The Abbe number on the d-line basis of the lens on the object side forming the i-th cemented lens from the object side is νai,
The Abbe number based on the d-line of the image-side lens that forms the i-th cemented lens from the object side is νbi,
The distance on the optical axis from the aperture stop to the cemented surface of the i-th cemented lens from the object side is Dci,
When the radius of curvature of the cemented surface of the i-th cemented lens from the object side is Rci,

An objective lens for an endoscope that satisfies the conditional expression (1) represented by The combined focal length of the first lens group and the second lens group is f12,
The focal length of the third lens group is f3,
The radius of curvature of the image-side surface of the negative lens of the first lens group is Rr1,
The radius of curvature of the object-side surface of the negative lens of the first lens group is Rf1,
The radius of curvature of the image side surface of the negative lens of the second lens group is Rr2,
When the radius of curvature of the object-side surface of the negative lens of the second lens group is Rf2,

The objective lens for an endoscope according to claim 1, wherein the conditional expression (2) expressed by The radius of curvature of the most image-side surface of the third lens group is Rr3,
When the focal length of the endoscope objective lens is f,
-20<Rr3/f<-0.5 (3)
The objective lens for an endoscope according to claim 1 or 2, which satisfies the conditional expression (3). The radius of curvature of the most image-side surface of the fourth lens group is Rr4,
When the focal length of the endoscope objective lens is f,
-2.5<Rr4/f<-1 (4)
The objective lens for an endoscope according to any one of claims 1 to 3, which satisfies the conditional expression (4) represented by: The radius of curvature of the image-side surface of the fifth lens group is Rr5,
When the radius of curvature of the most object-side surface of the fifth lens group is Rf5,
-0.5<(Rr5+Rf5)/(Rr5-Rf5)<1 (5)
The objective lens for an endoscope according to any one of claims 1 to 4, which satisfies the conditional expression (5) represented by: The distance on the optical axis from the aperture stop to the lens surface closest to the object is Df,
When the distance on the optical axis from the aperture stop to the lens surface closest to the image is Dr,
0.5<Df/Dr<1.5 (6)
The objective lens for an endoscope according to any one of claims 1 to 5, which satisfies the conditional expression (6) represented by: The combined focal length of the first lens group, the second lens group, and the third lens group is f123,
When the combined focal length of the fourth lens group and the fifth lens group is f45,
1.5<|f123/f45|<10 (7)
The objective lens for an endoscope according to any one of claims 1 to 6, which satisfies the conditional expression (7) represented by:
The objective lens for an endoscope according to claim 1, wherein the conditional expression (1-1) represented by the following is satisfied.
The objective lens for an endoscope according to claim 2, wherein the conditional expression (2-1) represented by the following is satisfied. -12<Rr3/f<-1 (3-1)
The objective lens for an endoscope according to claim 3, wherein the conditional expression (3-1) represented by the following is satisfied. -2.2<Rr4/f<-1.2 (4-1)
The objective lens for an endoscope according to claim 4, wherein the conditional expression (4-1) represented by the following is satisfied. -0.25<(Rr5+Rf5)/(Rr5-Rf5)<0.7 (5-1)
The objective lens for an endoscope according to claim 5, which satisfies the conditional expression (5-1) represented by: 0.8<Df/Dr<1.2 (6-1)
The objective lens for an endoscope according to claim 6, which satisfies the conditional expression (6-1) represented by: 1.8<|f123/f45|<8 (7-1)
The objective lens for an endoscope according to claim 7, which satisfies the conditional expression (7-1) represented by: An endoscope comprising the endoscope objective lens according to claim 1.