JPH11125770A - Zoom image pickup optical system for endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an image pickup optical system suitable to constitute a rigid endoscope field conversion system by optical image segmenting by providing a 4th lens group nearest to an image side with a lens group which does not contribute to variable power and providing the 4th lens group with at least one surface intended to perform the adjustment of the variable power or the adjustment of the position of an exit pupil. SOLUTION: This optical system is constituted of a 1st lens group G1 having a positive focal distance and performing focusing by moving an entire lens group or partially moving lens components in the lens group in an optical axis direction, a 2nd lens group G2 having a negative focal distance and moving in the optical axis direction in the case of the variable power, a 3rd lens group G3 having the positive focal distance and moving in the optical axis direction in the case of the variable power, and the 4th lens group G4 always fixed in order from an endoscope side. Then, it satisfies conditions (1) 0.3<β4 <3, (2) -1.2<f2 /fW<-0.5, and (3) -1.3<f2 /f3 <-0.5. In the expressions, β4 is the paraxial lateral magnification of the 4th lens group, fW is the focal distance of an entire system at a wide end, and f2 and f3 are the focal distances of the 1st and the 2nd lens groups.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a zoom image pickup optical system used for an image pickup apparatus connectable to an eyepiece of an endoscope.

[0002]

2. Description of the Related Art As an endoscope for transmitting images optically,
There are a fiberscope using an image guide fiber and a rigid scope using a relay lens. These endoscopes are provided with eyepieces on the eyepiece side so that eyepiece observation is possible. By connecting an imaging device having an imaging optical system and an imaging device to such a fiberscope or an eyepiece of a rigid endoscope, an endoscope image can be observed on a television monitor.

In recent years, with the spread of endoscopic surgery, image observation on a television monitor has become essential. In particular, observation with a television monitor using a rigid scope having a higher resolution than a fiberscope is mainly used.

FIG. 19 is a diagram showing an outline of an apparatus for connecting an imaging device to a rigid endoscope and projecting the image on a monitor.
In the figure, 1 is a rigid endoscope, 2 is an eyepiece of the rigid endoscope, 3 is an adapter, and 4 is a television camera. As shown in this figure, an adapter 3 is attached to the eyepiece 2 of the rigid endoscope 1, and a television camera is further attached. In this way, the object image 11 formed by the objective lens provided in the rigid endoscope 1 is enlarged by the eyepiece 12 arranged in the eyepiece 2, and the object image 11 in the television camera 4 is formed by the photographing optical system 13 of the adapter 3. An image is formed on the image pickup device 14 provided in the. The image formed on the image sensor 14 is signal-processed by the camera control unit 5 and then displayed on the television monitor 6. Reference numeral 15 denotes a filter group including an infrared cut filter, an optical low-pass filter, and the like.

In the apparatus shown in FIG. 19, an object image having a desired field of view can be displayed according to a procedure or an endoscope by appropriately selecting and attaching an adapter having an imaging optical system having a different focal length. . However, for example, when it is desired to change the size of the visual field or the observation magnification during the operation, it is troublesome to replace the adapter with the required visual field or magnification. Therefore, an adapter having a zoom function is desired.

There is also a device having a configuration in which an adapter and a television camera are integrated, and in such a device, an adapter having a zoom function is desired.

[0007] An adapter having a zoom function used in an image pickup apparatus connected to such an endoscope also requires an increase in the zoom ratio, as in the case of a general zoom lens.

[0008] Further, since the image of the hard endoscope is transmitted only through the lens system, by providing the imaging optical system 13 with a focus function, it is possible to perform an optimum focus adjustment for the observation object. For this reason, an imaging device (adapter) is often provided with a focus function.

A conventional example of an endoscope imaging optical system having a zoom function and a focus function as described above is disclosed in
An optical system described in JP-A-90503 is known. In this conventional example, focusing is performed in a front group by a three-group zoom including a positive, a negative, and a positive lens group.

However, this conventional example has a zoom ratio of 1.9.
The zoom ratio cannot be increased with the lens having the configuration of the conventional example.

Japanese Patent Application Laid-Open Nos. 9-28663 and 8-33 disclose conventional examples provided with a rigid scope conversion system in order to greatly improve the working efficiency of endoscopic surgery.
An apparatus disclosed in Japanese Patent No. 2169 is known.

FIG. 20 shows an image pickup apparatus having the above-mentioned visual field conversion system. In FIG. 20, reference numeral 16 denotes a zoom image pickup optical system, and reference numeral 17 denotes an image pickup unit capable of moving in a direction perpendicular to the optical axis. The imaging unit 17 includes a filter group 18 including an infrared cut filter, an optical low-pass filter, and the like. This imaging unit 17
Is mounted on an XY linear stage (not shown), and this linear stage is driven using a motor or the like.

FIG. 21 is a conceptual diagram of the field of view conversion.
Indicates the wide side, and (B) indicates the tele side. On the wide side, an optical image close to the size of the imaging range is obtained. On the other hand, on the telephoto side, an optical image larger than the imaging range is formed in order to perform the visual field conversion, and the visual field conversion is performed by shifting the imaging range within the range of the optical image. In other words, in the figure, the image is widened as the final image 23 on the telephoto side in FIG. 3B, and the imaging range 21 is moved as shown by the arrow in the view of FIG. Perform the conversion.

In the rigid-field-of-view conversion system based on optical image clipping described in the above-mentioned conventional example, the operation of moving the position of the rigid endoscope is reduced as the operator increases the zoom ratio. Expansion is required. In addition, in the rigid-scope field-of-view conversion system, on the tele side of the zoom, since the imaging device moves in the image of the enlarged rigid mirror, the design image height on the tele side is optically designed according to the zoom ratio. Must be bigger. As a result, it becomes extremely difficult to correct the aberration of the image pickup optical system, and a satisfactory optical performance cannot be obtained with the configuration of the zoom lens described in Japanese Patent Application Laid-Open No. Hei 4-90503.

[0015]

SUMMARY OF THE INVENTION The present invention relates to a zoom imaging optical system having a focus function of an imaging device which is used by being attached to various endoscopes, and which can be used even when the zoom ratio exceeds 2. An image pickup optical system is provided.

An object of the present invention is to provide a zoom image pickup optical system which is particularly suitable for configuring a rigid-field-of-view conversion system by clipping an optical image.

[0017]

An imaging optical system for an endoscope according to the present invention focuses by moving an entire lens group or a part of lens components in the lens group in the optical axis direction in order from the endoscope. A first lens group having a positive focal length, a second lens group having a negative focal length that moves in the optical axis direction during zooming, and a third lens group having a positive focal length that moves in the optical axis direction during zooming. And a fourth lens group which is always fixed, and satisfies the following conditions (1), (2) and (3). (1) 0.3 <β ₄ <3 (2) −1.2 <f ₂ / f _W <−0.5 (3) −1.3 <f ₂ / f ₃ <−0.5 where β ₄ is the focal length of the fourth paraxial lateral magnification of the lens group, f _W is the total focal length at the wide end, f _2, f ₃ are each the first lens group and the second lens group.

The feature of the optical system of the present invention is that
A lens group in which the lens group does not contribute to zooming is provided.
That is, at least one surface for adjusting the magnification or adjusting the position of the exit pupil is provided in the lens group. This surface makes it possible to control the power arrangement independently of the aberration correction, thereby increasing the degree of freedom of the aberration correction,
A zoom optical system with an unprecedented high zoom ratio can be realized. Alternatively, a cemented lens may be used in the fourth lens unit, or bending may be performed to control the power balance between both end surfaces in order to control aberration on each surface in the lens unit, thereby providing a degree of freedom of aberration correction. Has been raised.

A conventional three-group zoom imaging optical system for an endoscope is
The reason that the zoom ratio cannot be enlarged is that the position of the entrance pupil is restricted when this optical system is combined with an endoscope.

Normally, since the endoscope imaging optical system does not have a brightness stop, the aperture of the image forming light beam is determined by the exit pupil diameter of the endoscope. The eye point of the endoscope is generally set at a position where there is no problem in visual observation, and is only a few mm away from the end face of the eyepiece. For that purpose, the position of the entrance pupil of the imaging optical system must be set to a position close to the endoscope, and the zoom optical system of the fixed aperture stop must be used. This greatly restricts aberration correction when the zoom ratio is enlarged.

In the three-unit zoom optical system, it is possible to secure a required zoom range, but it is necessary to control the balance of the power of each lens unit for correcting the Petzval sum and to control the entire zoom range. At least one of the control of the exit pupil position and the control of the aberration becomes impossible to control. for that reason,
Forcibly securing specifications required for the optical system including the pupil position makes it difficult to correct aberrations of the optical system.

Therefore, in the optical system of the present invention, the fourth lens group satisfies the condition (1).

Condition (1) is a condition relating to the image magnification of the fourth lens group of the optical system of the present invention. This fourth lens group is a lens group that plays an additional role to the three-group zoom optical system. Therefore, it is necessary to prevent the fourth lens group from having a strong effect on image formation.

There is known a four-group zoom optical system for a film camera in which the third lens group is afocal. However, in an optical system having a configuration in which the entrance pupil is extremely forward, such as the optical system of the present invention, if the fourth lens group furthest from the pupil has an image-forming action, the aberration is contrary to the object of the present invention. Correction becomes difficult. Therefore, it is not desirable to make the fourth lens group have an image-forming action by afocaling up to the third lens group as described above.

In the present invention, the magnification of the fourth lens unit is set in the range shown in the condition (1) so that the fourth lens unit does not have an extreme convergence or divergence.

When the value goes below the lower limit of 0.3 to condition (1), the fourth condition
The convergence action of the lens group becomes too strong, and if it exceeds the upper limit of 3, the divergence action becomes too strong, and in any case, the effect of the fourth lens group introduced for the purpose of aberration correction cannot be obtained.

The first to third lens groups in the zoom optical system according to the present invention have a well-known configuration as described below.

The first lens group closest to the endoscope is a lens group used for focusing, and can perform focusing independent of the zoom state.

The second lens group and the third lens group perform magnification and correction of the image position at the time of magnification by moving in the optical axis direction, similarly to a general zoom lens. In order to increase the zoom ratio with a relatively simple configuration, the first to third lens units are composed of positive, negative, and positive lens units, and the negative second lens unit is moved. It is effective to perform zooming and correct the image position with either the positive first lens unit or the third lens unit. In the present invention, the image position is corrected by moving the third lens unit during zooming in order to provide the first lens unit with a focusing function. The third lens group is designed to contribute not only to the correction of the image position but also to the magnification.

In the first to third lens groups described above,
In the present invention, the conditions (2) and (3) are satisfied for the second and third lens groups.
Was satisfied.

These conditions (2) and (3) relate to the moving range of the second lens unit and the third lens unit and the Petzval sum. It is preferable that the moving range of the lens unit during zooming be small, because the frame design becomes easy. Also, the smaller the focal lengths f ₂ and f _{3 of} the second and third lens groups, the smaller the moving range, which is preferable in design. However, if the power of the second lens group becomes too strong, the Petzval sum tends to be overcorrected, which is not preferable. If the power of the second lens group does not become too strong, the Petzval sum can be controlled by the power balance between the second lens group and the third lens group. For this purpose, the power of the second lens group must be set to the condition (2).
It is desirable that the power balance between the second lens group and the third lens group be set so as to satisfy the condition (3).

When the value goes below the lower limit of -1.2 of the condition (2), the power of the second lens unit becomes weak, and the moving range of the second lens unit at the time of zooming becomes large. The upper limit is -0.5
When the value exceeds, the power of the second lens group becomes strong, and it becomes difficult to correct the Petzval sum. The lower limit of condition (3) is -1.
If it exceeds 3, the Petzval sum becomes insufficiently corrected and the upper limit is −
If it exceeds 0.5, the Petzval sum becomes overcorrected.

In the zoom optical system according to the present invention, it is more preferable that the following condition (4) is satisfied. (4) 0.7 <β _2W / β _3W <1.4 where β _2W and β _3w are paraxial lateral magnifications of the second lens unit and the third lens unit, respectively, at the wide ends.

The condition (4) is provided to keep the range of movement of both the lens units during zooming by keeping the balance of the contribution of the second lens unit and the third lens unit to zooming. Condition.

The simplest configuration for zooming includes a configuration in which the negative second lens unit is used as a variator and the positive third lens unit is used as a compensator. However, in this case, the amount of movement of the second lens group becomes large, which adversely affects the frame design such as setting the rotation angle of the cam. For this reason, it is desirable to use the third lens group in a magnification range that can contribute to zooming without using a pure compensator. In the wide-angle end state, if the magnifications of the second lens unit and the third lens unit are made as close as possible, the third lens unit can be given a property close to a variator, and the movement range of both lens units can be balanced. Easy to take.

When the value exceeds the upper limit of 1.4 of the condition (4), the second condition is satisfied.
If the amount of movement of the lens group is too large, and if the lower limit of 0.7 of the condition (4) is exceeded, the amount of movement of the third lens group will be too large.

In the zoom image pickup optical system according to the present invention, it is preferable that the zoom range includes a state in which the paraxial lateral magnification of the second lens unit and the third lens unit becomes substantially -1 at the same time.

As described above, both lens groups are almost simultaneously
By including the state of 1x, the second lens group and the third
Defocusing at the time of zooming due to backlash in the cam groove of the lens group can be reduced.

When the user performs a zoom operation, both lens groups move, but finally the position where each lens group comes to rest varies due to the play of the cam groove. Since this play causes a focus shift, it is desirable to reduce the sensitivity of the focus shift due to minute movement of each lens group in the optical axis direction. When a certain lens group has a paraxial lateral magnification close to -1, the focus hardly changes even when the lens group is moved in the optical axis direction, and the sensitivity of defocusing is as follows. Increases with distance from the object. for that reason,
If the second lens group and the third lens group that move for zooming have a state in which the paraxial lateral magnification becomes approximately -1 at the same time within the zooming range, the second lens group and the third lens group move within the zooming range. , The third lens group always has a magnification close to −1,
Defocus at the time of zooming can be reduced. Even if both the second lens unit and the third lens unit include -1x within the zooming range, if both lens units do not become approximately -1x at the same time, focus movement at the time of zooming will occur even at the time of design. Not preferred.

In the zoom imaging optical system according to the present invention, it is desirable that the first, second, and third lens groups have the following configurations.

The first lens group includes one positive lens and one negative lens having an Abbe number smaller than the positive lens, and the second lens group has one positive lens and a lower refractive index than the positive lens. In addition, it is composed of one cemented lens component composed of one negative lens having low dispersion. The cemented surface of this cemented lens has a positive refractive power. The third lens group includes three or more lens components, one of which includes a negative lens made of a material having an Abbe number of 40 or less, and at least one of the lens components includes It is desirable that the cemented lens has a cemented surface having a negative refractive power.

The above-mentioned lens component refers to a single lens or a cemented lens arranged with an air gap therebetween.

In the design of the zoom lens, it is necessary to reduce the aberration in each lens group in order to reduce the aberration over the entire zoom range.

In the optical system of the present invention, the correction of distortion is not a problem because the angle of view is narrow, and the curvature of field is roughly determined by the power distribution of each lens unit. It has little to do with field curvature. Therefore, other aberrations are reduced by the first lens group, the second lens group, and the third lens group.
It is necessary to reduce the size of each lens group independently.

In the zoom image pickup optical system according to the present invention, it is desirable that the first lens group includes one positive lens and one negative lens having an Abbe number smaller than the positive lens as described above.

The reason why the first lens group is configured as described above is that it is effective in correcting spherical aberration, coma, and axial chromatic aberration. In the first lens group, since the principal ray height is low, it is not necessary to pay much attention to correction of astigmatism and chromatic aberration of magnification. If the first lens group is not configured as described above, the correction of the aberrations in this lens group becomes insufficient, and it becomes difficult to correct the aberrations in the entire system in the entire zoom range.

It is desirable that the second lens group has the above-described configuration in order to favorably correct spherical aberration, astigmatism, coma aberration, and chromatic aberration in the lens group. Since the second lens group is sandwiched between the first lens group and the third lens group that is a moving lens group, a spatial margin cannot be obtained. Therefore, the entire lens group is simplified to reduce the thickness and reduce aberration. It must be well corrected. For that purpose, it is desirable to constitute only one cemented lens.

Further, by introducing a cemented surface having a positive refractive power into the second lens unit having a negative power, spherical aberration, astigmatism and coma which tend to be overcorrected can be complementarily corrected. Further, since the second lens group has a particularly strong power in the entire system, it is necessary to consider the material used for the lens.

Next, in order to correct spherical aberration, astigmatism, coma, and chromatic aberration in the third lens group, it is desirable that the third lens group is configured as follows.

In order to correct spherical aberration and coma,
It is necessary to provide three or more lens components that can be bent with air contact surfaces on both sides. Further, at least one cemented surface having a negative refractive power is required to correct astigmatism. In order to correct chromatic aberration, it is necessary to provide at least one negative lens made of a material having an Abbe number of 40 or less.

For the above reasons, in the zoom image pickup optical system according to the present invention, it is desirable that the third lens group has the above-described configuration.

If the above configuration is not adopted, the correction of the aberrations in the third lens group becomes insufficient, and the correction of the aberrations in the entire system in the entire zoom range becomes difficult.

In the zoom photographing optical system having the basic structure of the present invention and other structures, the following conditions (5) and (5) are satisfied.
It is desirable to satisfy (6), (7), and (8). (5) n _2P > 1.7 (6) 0.03 <n _2P −n _2N <0.15 (7) ν _2P <35 (8) ν _2N −ν _2P > 15 where n _2P and n _2N are Refractive indexes of the positive lens and the negative lens of the second lens group, and ν _2P and ν _2N are Abbe numbers of the positive lens and the negative lens of the second lens group, respectively.

The conditions (5) to (8) correspond to the second
This is for correcting spherical aberration, astigmatism, coma aberration, and chromatic aberration in the lens group.

If the conditions (5) and (6) are not satisfied, the second condition
Correction of astigmatism and coma in the lens group becomes insufficient. Further, the Petzval sum may be excessively corrected.

If the conditions (7) and (8) are not satisfied, the correction of chromatic aberration in the second lens group becomes insufficient, and it becomes difficult to correct the chromatic aberration of the entire system in the entire zoom range.

In the zoom imaging optical system having the basic structure of the present invention and all the other structures described above, it is desirable that the paraxial lateral magnification of the fourth lens group be less than 1. This is to reduce a focus shift at the time of zooming due to backlash in the cam groove between the second lens unit and the third lens unit.

The focus sensitivity of the second and third lens units is related to the magnification of the fourth lens unit. If the paraxial lateral magnification of the fourth lens group is set to less than 1 to provide a reduction system, the second lens group and the third
The focus sensitivity of the lens group is reduced in proportion to the square of the paraxial lateral magnification of the fourth lens group, and the focus shift during zooming can be reduced. Conversely, if the fourth lens group is a magnifying system,
It is not preferable because the focus sensitivity of the lens group is increased and the focus shift during zooming due to backlash in the cam groove increases.

For the above reasons, it is desirable that the fourth lens group satisfies the following condition (1 ') instead of the condition (1). (1 ′) 0.3 <β ₄ <1

This condition is a condition in which the upper limit of the condition (1) is narrowed. By this, it is possible to reduce the focus shift at the time of zooming due to backlash in the cam grooves of the second lens unit and the third lens unit.

If the upper limit of 1 to condition (1 ′) is exceeded, the fourth condition
Since the lens group becomes a magnifying system and the focus sensitivity of the second lens group and the third lens group is expanded, the focus shift at the time of zooming due to backlash in the cam groove increases.

The zoom imaging optical system of the present invention is very useful if applied to a rigid-scope field-of-view conversion system based on optical image clipping. Therefore, in the optical system of the present invention,
A solid-state imaging unit that can move in the direction perpendicular to the optical axis is placed near the image position, and if this solid-state imaging unit is moved to convert the field of view, an imaging optical system most suitable for a rigid mirror field-of-view conversion system is realized. I can do it.

[0063]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described based on respective examples.

Each embodiment of the zoom imaging optical system according to the present invention
The following data is shown in FIGS. Example 1 f = 14.359~24.447~40.988 (13.281~45.664) virtual aperture inner diameter = 4.400, Length = 67.282 zoom ratio = 2.85, the entrance pupil position _{= 4.561 r 1 = ∞ d 1} = 1.0000 n 1 = 1.51633 ν 1 = 64.15 r ₂ = ∞ d ₂ = 5.0000 r ₃ = 18.7470 d ₃ = 1.4000 n ₂ = 1.80610 ν ₂ = 40.92 r ₄ = -18.7470 d ₄ = 0.7000 n ₃ = 1.74077 ν ₃ = 27.79 r ₅ = 42.5620 d ₅ = D ₁ (variable) r ₆ = -14.2800 d ₆ = 1.9000 n ₄ = 1.84666 ν ₄ = 23.78 r ₇ = −6.0580 d ₇ = 0.9000 n ₅ = 1.79090 ν ₅ = 44.20 r ₈ = 25.7970 d ₈ = D ₂ (variable) r ₉ = ∞ d ₉ = 3.1500 n ₆ = 1.72916 v ₆ = 54.68 r ₁₀ = -23.4520 d ₁₀ = 0.2000 r ₁₁ = 44.8460 d ₁₁ = 5.0500 n ₇ = 1.72916 v ₇ = 54.68 r ₁₂ = -17.8940 d ₁₂ = 1.6000 n ₈ = 1.84666 v ₈ = 23.78 r ₁₃ = -111.2400 d ₁₃ = 0.2000 r ₁₄ = 12.4220 d ₁₄ = 4.4000 n ₉ = 1.58913 ν ₉ = 61.14 r ₁₅ = 35.5110 d ₁₅ = 0.3000 r ₁₆ = 19.8230 d ₁₆ = 2.7000 n _{1 0 = 1.58913 ν 10 = 61.14 r} 17 = ∞ d 17 = 1.4000 n 11 = 1.83400 ν 11 = 37.16 r 18 = 9.3060 d 18 = D 3 ( _{variable) r 19 = 10.6910 d 19 =} 3.5000 n 12 = 1.69895 ν 12 = _{30.13 r 20 = ∞ d 20 =} 1.2000 n 13 = 1.80100 ν 13 = 34.97 r 21 = 14.0560 d 21 = 1.8000 r 22 = ∞ d 22 = 1.6000 n 14 = 1.51399 ν 14 = 74.00 r 23 = ∞ d 23 = 2.0000 r ₂₄ = ∞ d ₂₄ = 0.7500 n ₁₅ = 1.51633 ν ₁₅ = 64.14 r ₂₅ = ∞ d ₂₅ = 0.9600 r ₂₆ = ∞ (image) f Image height FD ₁ D ₂ D ₃ 14.359 (f _W ) 1.718 3.228 3.9190 18.0935 2.7399 _{24.447 (f S) 2.937 5.544 7.9760} 10.5529 6.2235 40.988 (f T) 5.086 9.647 11.0857 2.8270 10.8398 13.281 (f WM) 1.718 2.985 3.2320 19.2145 2.3060 45.664 (f TM) 5.086 10.905 11.6583 1.0590 12.0351 f D 1 D 2 D 3 β 2 β ₃ 14.359 3.9190 18.0935 2.7399 -0.751 -0.775 15.147 4.3749 17.3302 3.0473 -0.773 -0.795 15.983 4.8210 16.5669 3.3646 -0.795 -0.816 16.868 5.2570 15.8036 3.6919 -0.818 -0.837 17.80 3 5.6829 15.0402 4.0293 -0.842 -0.858 18.793 6.0985 14.2769 4.3771 -0.867 -0.881 19.837 6.5037 13.5136 4.7352 -0.893 -0.904 20.939 6.8984 12.7503 5.1038 -0.919 -0.928 22.100 7.2827 11.9869 5.4828 -0.946 -0.952 23.322 7.6564 11.2236 7.9725 -24 10.4603 6.2726 -1.004 -1.003 25.953 8.3721 9.6969 6.6834 -1.033 -1.030 27.365 8.7142 8.9336 7.1046 -1.064 -1.057 28.841 9.0459 8.1703 7.5362 -1.096 -1.085 30.383 9.3673 7.4070 7.9782 -1.128 -1.113 31.991 9.6784 6.6436 8.4304 -3.1639.94 -42. -1.196 -1.172 35.400 10.2704 5.1170 9.3650 -1.231 -1.203 37.201 10.5517 4.3537 9.8471 -1.267 -1.234 39.064 10.8234 3.5903 10.3387 -1.303 -1.266 40.988 11.0857 2.8270 10.8398 -1.341 -1.298 f W = 14.359, f 1 = 33.481, f 2 = - 12.237, f ₃ = 15.498, f ₄ = 53.913 f _C = 33.481, β _2W = -0.751, β _3W = -0.775, β ₄ = 0.705 f ₁ / f _W = 2.332, f ₂ / f _W = -0.852, f ₃ / f _W = 1.079 f ₄ / f _W = 3.755, f ₂ / f ₃ = -0.790, f _C / f _W = 2.332 β _2W / β _3W = 0.969, n _2P −n _2N = 0.0608, ν _2N −ν _2P = 20.42

Example 2 f = 14.295 to 39.620 Inner diameter of virtual stop = 5.000, overall length = 63.949 Zoom ratio = 2.77, entrance pupil position = 4.881 r ₁ = ∞d ₁ = 1.0000 n ₁ = 1.51633 ν ₁ = 64.15 r ₂ = Ｄ d ₂ = 4.6379 r ₃ = 15.7592 d ₃ = 1.5000 n ₂ = 1.48749 ν ₂ = 70.23 r ₄ = -40.6457 d ₄ = 1.5000 r ₅ = -35.9574 d ₅ = 1.0000 n ₃ = 1.84666 ν ₃ = 23.78 r ₆ = -641.0854 d ₆ = D ₁ (variable) r ₇ = -18.7678 d ₇ = 2.5000 n ₄ = 1.84666 ν ₄ = 23.78 r ₈ = -7.0000 d ₈ = 1.2000 n ₅ = 1.77250 ν ₅ = 49.60 r ₉ = 22.9879 d ₉ = D ₂ (variable) r ₁₀ = -778.8880 d ₁₀ = 2.7694 n ₆ = 1.48749 ν ₆ = 70.23 r ₁₁ = -23.9900 d ₁₁ = 0.3000 r ₁₂ = 26.5232 d ₁₂ = 3.3172 n ₇ = 1.58913 ν ₇ = 61.14 r _{13 = -47.6765 d 13 = 0.3000 r 14} = 18.5549 d 14 = 5.0000 n 8 = 1.51633 ν 8 = 64.14 r 15 = -34.9549 d 15 = 1.8000 n 9 = 1.84666 ν 9 = 23.78 r 16 = 65.8593 d 16 = 0.3000 r 17 _{10.4752 d 17 = 4.2707 n 10 =} 1.72916 ν 10 = 54.68 r 18 = ∞ d 18 = 1.8000 n 11 = 1.83400 ν 11 = 37.16 r 19 = 6.9568 d 19 = D 3 ( _{variable) r 20 = -69.5104 d 20 =} 2.1213 n ₁₂ = 1.83400 v ₁₂ = 37.16 r ₂₁ = -32.0947 d ₂₁ = 2.0000 r ₂₂ = ∞ d ₂₂ = 1.6000 n ₁₃ = 1.51399 v ₁₃ = 74.00 r ₂₃ = ∞ d ₂₃ = 0.5000 r ₂₄ = ∞ d ₂₄ = 0.7500 n ₁₄ = 1.51633 ν ₁₄ = 64.14 r ₂₅ = ∞ d ₂₅ = 0.9600 r ₂₆ = ∞ (image) f Image height FD ₁ D ₂ D ₃ 14.295 (f _W ) 1.697 2.813 2.2000 17.0878 3.0350 39.620 (f _T ) 5.090 8.117 11.6487 2.1459 8.5281 f D ₁ D ₂ D ₃ β ₂ β ₃ 14.295 2.2000 17.0878 3.0350 -0.575 -0.558 17.388 4.4382 14.0994 3.7852 -0.632 -0.618 21.289 6.5536 11.1110 4.6581 -0.698 -0.688 26.175 8.5252 8.1227 5.6749 -0.773 -0.768 32.215 10.3175 5.1343 6.8710- 0.856 -0.864 39.620 11.6487 2.1459 8.5281 -0.931 -0.996 f W = 14.295, f 1 = 44.594, f 2 = -14.225, f 3 = 12.563, f 4 = 69.696 f C = 23.500, β _2W = -0.575, β _3W = -0.558, β ₄ = 0.942 f ₁ / f _W = 3.120, f ₂ / f _W = -0.995, f ₃ / f _W = 0.879 f ₄ / f _W = 4.876 , F ₂ / f ₃ = −1.132, f _C / f _W = 1.644 β _2W / β _3W = 1.030, n _2P −n _2N = 0.0742, ν _2N −ν _2P = 25.82

[0066] Example 3 f = from 16.928 to 41.318 virtual aperture inner diameter = 6.868, Length = 77.436 zoom ratio = 2.44, the entrance pupil position _{= 4.881 r 1 = ∞ d 1} = 3.0000 n 1 = 1.51633 ν 1 = 64.15 r 2 = ∞ d ₂ = 3.6810 r ₃ = 13.1870 d ₃ = 1.7500 n ₂ = 1.51633 ν ₂ = 64.15 r ₄ = -54.7020 d ₄ = 1.5000 n ₃ = 1.78472 ν ₃ = 25.68 r ₅ = 82.2820 d ₅ = D ₁ (variable) _{r 6 = -18.3760 d 6 = 3.0000} n 4 = 1.84666 ν 4 = 23.78 r 7 = -6.5630 d 7 = 1.7000 n 5 = 1.77250 ν 5 = 49.60 r 8 = 16.1440 d 8 = D 2 ( variable) r ₉ = 40.6530 d ₉ = 2.0000 n ₆ = 1.84666 v ₆ = 23.78 r ₁₀ = 23.2870 d ₁₀ = 6.0000 n ₇ = 1.72916 v ₇ = 54.68 r ₁₁ = -36.5300 d ₁₁ = 0.3000 r ₁₂ = 62.0340 d ₁₂ = 5.9100 n ₈ = 1.80610 v _{8 = 40.95 r 13 = -20.0030 d} 13 = 2.0000 n 9 = 1.84666 ν 9 = 23.78 r 14 = ∞ d 14 = 0.3000 r 15 = 18.6320 d 15 = 7.0000 n 10 = 1.77250 ν 10 = 49.60 r 16 = ∞ d 16 = 2.0000 n ₁₁ = 1.78472 v ₁₁ = 25.68 r ₁₇ = 43.6890 d ₁₇ = D ₃ (variable) r ₁₈ = -25.9400 d ₁₈ = 1.5000 n ₁₂ = 1.51633 v ₁₂ = 64.15 r ₁₉ = ∞ d ₁₉ = 5.9400 r ₂₀ = _{∞ d 20 = 1.6000 n 13 =} 1.51399 ν 13 = 74.00 r 21 = ∞ d 21 = 2.0000 r 22 = ∞ d 22 = 0.7500 n 14 = 1.51633 ν 14 = 64.14 r 23 = ∞ d 23 = 0.9600 r 24 = ∞ ( Image) f Image height FD ₁ D ₂ D ₃ 16.928 (f _W ) 1.993 2.421 4.0241 15.5080 4.5124 41.318 (f _T ) 5.096 6.184 10.1361 2.0982 11.8102 f D ₁ D ₂ D ₃ β ₂ β ₃ 16.928 4.0241 15.5080 4.5124 -0.549- 0.611 20.278 5.8586 12.8261 5.3599 -0.602 -0.668 24.394 7.5539 10.1441 6.3465 -0.660 -0.735 29.381 9.0599 7.4621 7.5225 -0.723 -0.815 35.234 10.2313 4.7802 9.0331 -0.780 -0.917 41.318 10.1361 2.0982 11.8102 -0.775 -1.105 f W = 16.928, f 1 = 39.002 , F ₂ = -11.505, f ₃ = 14.761 f ₄ = -50.239, f _C = 39.002, β _2W = -0.549, β _3W = -0.611, β ₄ = 1.228 f ₁ / f _W = 2.304, f ₂ / f _W = -0.680, f ₃ / f _W = 0.872 f ₄ / f _W = -2.968, f ₂ / f ₃ = -0.779, f _C / f _W = 2.304 β _2W / β _3W = 0.899 , N _2P −n _2N = 0.0742, ν _2N −ν _2P = 25.82

Example 4 f = 14.180 to 41.250 Inner Diameter of Virtual Aperture = 5.000, Overall Length = 86.630 Zoom Ratio = 2.91, Entrance Pupil Position = 4.881 r ₁ = ∞ d ₁ = 3.0000 n ₁ = 1.51633 ν ₁ = 64.15 r ₂ = _{∞ d 2 = 5.0000 r 3 =} 18.9881 d 3 = 1.8000 n 2 = 1.48749 ν 2 = 70.23 r 4 = -47.0367 d 4 = 0.8000 n 3 = 1.80518 ν 3 = 25.42 r 5 = -159.1706 d 5 = D 1 ( variable ) R ₆ = -13.5097 d ₆ = 2.5000 n ₄ = 1.84666 ν ₄ = 23.78 r ₇ = −7.1390 d ₇ = 1.2000 n ₅ = 1.79216 ν ₅ = 54.68 r ₈ = 30.5672 d ₈ = D ₂ (variable) r ₉ = 32.9102 d ₉ = 7.0000 n ₆ = 1.48749 ν ₆ = 70.23 r ₁₀ = -17.0000 d ₁₀ = 1.8000 n ₇ = 1.83400 ν ₇ = 37.16 r ₁₁ = -34.9999 d ₁₁ = 0.3000 r ₁₂ = 192.1030 d ₁₂ = 1.8000 n ₈ = 1.83400 ν ₈ = 37.16 r ₁₃ = 32.8387 d ₁₃ = 5.6000 n ₉ = 1.48749 ν ₉ = 70.23 r ₁₄ = -37.3424 d ₁₄ = 0.3000 r ₁₅ = 60.2247 d ₁₅ = 3.7834 n ₁₀ = 1.58913 ν ₁₀ = 61.14 r ₁₆ =- 7 _{3.0024 d 16 = 0.3000 r 17 =} 28.9594 d 17 = 5.6000 n 11 = 1.48749 ν 11 = 70.23 r 18 = -41.8922 d 18 = 1.8000 n 12 = 1.83400 ν 12 = 37.16 r 19 = -152.4859 d 19 = D 3 ( variable _{) r 20 = 12.7558 d 20 =} 3.2000 n 13 = 1.48749 ν 13 = 70.23 r 21 = 18.0000 d 21 = 3.7681 r 22 = 26.3299 d 22 = 3.8566 n 14 = 1.48749 ν 14 = 70.23 r 23 = ∞ d 23 = 1.4000 n _{15 = 1.84666 ν 15 = 23.78 r} 24 = 11.4174 d 24 = 2.7000 r 25 = ∞ d 25 = 1.6000 n 16 = 1.51399 ν 16 = 74.00 r 26 = ∞ d 26 = 0.5000 r 27 = ∞ d 27 = 0.7500 n 17 = 1.51633 ν ₁₇ = 64.14 r ₂₈ = ∞ d ₂₈ = 0.9600 r ₂₉ = ∞ (image) f Image height FD ₁ D ₂ D ₃ 14.180 (f _W ) 1.688 2.790 2.9000 19.0026 2.9093 41.250 (f _T ) 5.053 8.504 19.0568 2.3000 3.4550 f D ₁ D ₂ D ₃ β ₂ β ₃ 14.180 2.9000 19.0026 2.9093 -0.570 -0.612 18.230 6.1314 14.3111 4.3694 -0.656 -0.684 24.082 9.3627 9.2904 6.1587 -0.773 -0.773 31.955 12.5941 4.318 1 7.8997 -0.941 -0.859 37.895 15.8255 2.0565 6.9298 -1.202 -0.811 41.250 19.0568 2.3003 3.4547 -1.663 -0.639 f W = 14.180, f 1 = 41.688, f 2 = -13.999, f 3 = 20.232 f 4 = -36.241, f C = 41.688, β _2W = -0.570, β _3W = -0.612, β ₄ = 0.926 f ₁ / f _W = 2.940, f ₂ / f _W = -0.987, f ₃ / f _W = 1.427 f ₄ / f _W =- _{2.556, f 2 / f 3 =} -0.692, f C / f W = 2.940 β 2W / β 3W = 0.931, n 2P -n 2N = 0.1175, ν 2N -ν 2P = 30.90

[0068] Example 5 f = 13.539 to 41.337 virtual aperture inner diameter = 5.000, Length = 70.674 zoom ratio = 3.05, the entrance pupil position _{= 4.881 r 1 = ∞ d 1} = 3.0000 n 1 = 1.51633 ν 1 = 64.15 r 2 = _{∞ d 2 = 5.8000 r 3 =} 18.3671 d 3 = 1.8000 n 2 = 1.48749 ν 2 = 70.23 r 4 = -15.7473 d 4 = 0.8000 n 3 = 1.83400 ν 3 = 37.16 r 5 = -28.7665 d 5 = D 1 ( variable ) R ₆ = -13.8273 d ₆ = 3.2000 n ₄ = 1.84666 ν ₄ = 23.78 r ₇ = -5.7489 d ₇ = 1.2000 n ₅ = 1.777250 ν ₅ = 49.60 r ₈ = 27.3038 d ₈ = D ₂ (variable) r ₉ = _{-79.6208 d 9 = 1.8000 n 6 =} 1.84666 ν 6 = 23.78 r 10 = 15.7000 d 10 = 6.0000 n 7 = 1.48749 ν 7 = 70.23 r 11 = -33.5310 d 11 = 0.3000 r 12 = 55.1239 d 12 = 4.0000 n 8 = 1.77250 v ₈ = 49.60 r ₁₃ = -42.8482 d ₁₃ = 0.3000 r ₁₄ = 36.9810 d ₁₄ = 3.4000 n ₉ = 1.77 250 v ₉ = 49.60 r ₁₅ = -172.9625 d ₁₅ = 0.3000 r ₁₆ = 27.4881 d ₁₆ = 4.8000 n ₁₀ = 1.72916 ν ₁₀ = 54.68 r ₁₇ = -41.9951 d ₁₇ = 1.8000 n ₁₁ = 1.84666 ν ₁₁ = 23.78 r ₁₈ = -99.1111 d ₁₈ = D ₃ (variable) r ₁₉ = 18.1724 d ₁₉ = 2.8000 n ₁₂ = 1.48749 ν _{12 = 70.23 r 20 = -26.8269 d 20} = 1.2000 n 13 = 1.83400 ν 13 = 37.16 r 21 = 10.2042 d 21 = 2.8000 r 22 = ∞ d 22 = 1.6000 n 14 = 1.51399 ν 14 = 74.00 r 23 = ∞ d 23 = 0.5000 r ₂₄ = ∞ d ₂₄ = 0.7500 n ₁₅ = 1.51633 v ₁₅ = 64.14 r ₂₅ = ∞ d ₂₅ = 0.9600 r ₂₆ = ∞ (image) f Image height FD ₁ D ₂ D ₃ 13.539 (f _W ) 1.610 2.666 3.1000 11.4692 6.4943 41.337 (f _T ) 5.287 8.437 17.5739 2.3000 1.1896 f D ₁ D ₂ D ₃ β ₂ β ₃ 13.539 3.1000 11.4692 6.4943 -0.924 -0.360 17.032 5.9948 8.6103 6.4585 -1.173 -0.358 21.436 8.8896 6.0563 6.1176 -1.603 -0.330 4.76 26.754 11.784 5.2771 -2.535 -0.262 33.076 14.6791 2.6570 3.7274 -6.046 -0.137 41.337 17.5739 2.3000 1.1896 15.689 0.067 f W = 13.539, f 1 = 30.086, f 2 = -12.633, _{3 = 12.406 f 4 = -16.061,} f C = 30.086, β 2W = -0.924, β 3W = -0.360, β 4 = 1.302 f 1 / f W = 2.222, f 2 / f W = -0.933, f 3 / f _W = 0.916 f ₄ / f _W = -1.186, f ₂ / f ₃ = -1.018, f _C / f _W = 2.222 β _2W / β _3W = 2.567, n _2P −n _2N = 0.0742, ν _2N −ν _2P = 25.82 where r ₁ , r ₂ ,... Are the radii of curvature of the respective lens surfaces, d
₁ , d ₂ ,... Are the thickness of each lens and the air gap, n
₁ , n ₂ ,... Are the refractive indices of each lens, ν ₁ , ν ₂ ,.
Is the Abbe number of each lens. F _W is the focal length of the entire lens system at the wide end, f _S is the focal length of the entire lens system in the intermediate state, f _T is the focal length of the entire lens system at the telephoto end, and f _WM is mechanical at the wide end. The focal length of the entire lens system at the movement limit, _fTM is the focal length of the entire lens system at the mechanical movement limit at the telephoto end, f ₁
The focal length of the first lens group, f ₂ is the focal length of the second lens group, f ₃ is the focal length of the third lens group, f ₄ is the focal length of the fourth lens group, f _C is the first lens group , Β _2W is the paraxial lateral magnification at the wide end of the second lens group, β _3W is the paraxial lateral magnification at the wide end of the third lens group, β
₄ is the paraxial lateral magnification of the fourth lens group, n _2P is the refractive index of the positive lens of the second lens group, n _2N is the refractive index of the negative lens of the second lens group, and ν _2P is the positive lens of the second lens group. Abbe number of ν _2N
Is the Abbe number of the negative lens in the second lens group. The unit of length such as focal length and radius of curvature is mm.

The first embodiment includes, in order from the endoscope side, a first lens group G1 having a positive focal length, a second lens group G2 having a negative focal length, and a third lens group G3 having a positive focal length. , And a fourth lens group G4. The first lens group and the fourth lens group are fixed, and the second and third lens groups are moved to perform zooming.

Each lens group is as follows. The first lens group G1 is a cemented lens of a positive lens and a negative lens, and the Abbe number of the negative lens is smaller than that of the positive lens. The second lens group G2 is a cemented lens of a positive lens and a negative lens, and the cemented surface has a positive refractive power. The third lens group G3 includes four lens components, a positive lens, a cemented lens, a positive lens, and a cemented lens. The positive lens of the cemented lens component on the endoscope side and the negative lens of the cemented lens component on the image side are Abbe numbers. Is 40 or less. The fourth lens group G4 includes one cemented lens component.

In the optical system of this embodiment, at the intermediate focal length, the second lens unit and the third lens unit become approximately -1 at the same time. The second lens group G for the logarithm of the focal length of the entire system
2. The position of the third lens group G3 changes monotonously as shown in FIG. 6, and has no inflection point. If the cam curve has an inflection point, the machining accuracy of the cam groove decreases, so it is desirable that there be no inflection point as in this embodiment. In this embodiment, the cam for moving the second lens group G2 or the third lens group G3 may be a linear cam.

FIG. 11 is a graph showing the second logarithm of the focal length of the entire system.
10 shows a change in magnification of the lens group G2 and the third lens group G3. In the optical system according to the first embodiment, the change in magnification of the second and third lens groups G2 and G3 is substantially uniform, and the third lens group G3 also greatly contributes to zooming.

The first lens group G1 is composed of one cemented lens component, and performs focusing by moving this lens component in the optical axis direction.

The fourth lens unit G4 is composed of one cemented lens component having a positive focal length, and prevents the exit pupil position from approaching the image on the telephoto side where the image height is high. The position can be moved away from the image, and problems such as shading can be avoided when combined with a solid-state imaging device.

The magnification of the fourth lens group G4 is of a reduction system. In addition to the fact that the second lens group G2 and the third lens group G3 are close to −1, the focus sensitivity of the variable power lens group is reduced. I have.

In the first embodiment, the zoom ratio is 2.85, but the zoom ratio can be further increased.

When the zoom operation is motorized in the zoom optical system, it is necessary to allow a margin in the mechanical movement range when software controlling the stop positions of the wide end and the tele end. In the first embodiment, the zoom ratio is set to 2.85 in consideration of software control. However, when operating a machine, the zoom ratio can be made to function as a zoom optical system having a zoom ratio of 3.44.

In the second embodiment, as shown in FIG. 2, the first lens group G1 is composed of two lens components, a positive lens and a negative lens, which are separately disposed, and the third lens group G3 is an endoscope. The fourth embodiment differs from the first embodiment in that, in order from the side, the fourth lens unit G4 includes four lens components of a positive lens, a positive lens, a cemented lens, and a cemented lens, and the fourth lens group G4 includes a positive single lens. Further, as is clear from FIG. 7, which shows the relationship between the logarithm of the focal length of the entire system and the position of the second and third lens groups G2 and G3 in this embodiment, the movement of these lens groups is as follows.
This is the same as the first embodiment. FIG. 12 shows the relationship between the logarithm of the focal length of the entire system and the magnification of the second and third lens groups G2 and G3 in this embodiment. In the vicinity, the value is close to -1 times.

In the second embodiment, focusing is performed by moving only the endoscope-side positive lens L1 of the first lens group G1. Further, since the focal length of the positive lens of the movable lens that performs focusing with respect to the focal length of the entire first lens group can be shortened, the moving range at the time of focusing can be reduced.

The fourth lens group G4 including one positive lens can avoid problems such as shading when combined with a solid-state imaging device.

In the third embodiment, the third embodiment is configured as shown in FIG.
The fourth embodiment differs from the first embodiment in that the lens unit G3 includes three cemented lens components, and the fourth lens unit G4 includes one negative single lens component.

This embodiment is an optical system having a smaller zoom ratio but a larger entrance pupil diameter than the other embodiments and is bright.

The position of the second lens group G2 and the position of the third lens group G3 with respect to the logarithm of the focal length of the entire system in this embodiment is clear from FIG.
The second lens group has an extreme value near the telephoto end, and has a role somewhat like a compensator.

Further, the second and second logarithms of the focal length of the entire system are
From FIG. 13 showing the relationship between the magnifications of the third lens groups G2 and G3, only the third lens group G3 is configured to move across −1, and the contribution of the third lens group G3 to zooming is as follows. Second
A little larger than the lens group G2.

Further, the fourth lens group G4 is a concave negative lens in order to extend the focal length of the entire system as a magnifying system.

In the fourth embodiment, the third lens group G3 is composed of four lens components, a cemented lens component, a cemented lens component, a single lens component, and a cemented lens component, from the endoscope side, as shown in FIG. The fourth embodiment differs from the first embodiment in that the fourth lens group includes a single lens component and a cemented lens component.

In this embodiment, as shown in FIG. 9 showing the relationship between the logarithm of the focal length of the entire system and the position of the second and third lens groups G2 and G3, the movement of the third lens group G3 is close to the telephoto end. This lens group has an extreme value and plays a role close to a compensator.

Further, from the relationship between the logarithm and the logarithm of the focal length of the entire system shown in FIG. 14, only the second lens group G2 is moved by -1 times, and the magnification of the third lens group G3 is changed. Is slightly smaller than the second lens group G2.

The focal length of the fourth lens group G4 is negative. However, it is divided into two lens components, and positive power is collected on the endoscope side to make a reduced system. Further, a high dispersion negative lens is arranged in the fourth lens group G4 to correct lateral chromatic aberration. Further, by dividing the lens component into two lens components and making the endoscope-side surface of these lens components convex, the fluctuation of astigmatism during zooming is corrected.

In the fifth embodiment, as shown in FIG. 5, the third lens group G3 is composed of four lens components of a cemented lens component, a single lens component, a single lens component, and a cemented lens component in this order from the endoscope side. This is different from the first embodiment in the point.

In the fifth embodiment, as can be seen from FIG. 10 showing the relationship between the logarithm of the focal length of the entire system and the positions of the second and third lens groups G2 and G3, the second lens group G2 is a variator and the third lens group is a third lens group. Group G3 is the compensator.
Further, as can be seen from the relationship between the logarithm of the focal length of the whole system and the magnification in FIG. 15, the absolute value of the magnification of the third lens group G3 tends to decrease toward the telephoto side.

A chromatic aberration of magnification is corrected by disposing a cemented lens having a difference in dispersion in the fourth lens group G4. Astigmatism is corrected.

In each of the embodiments, the object distance is 1000 mm (diopter -1 / m) from the first surface toward the endoscope. Further, a parallel flat plate is disposed closer to the endoscope than the first lens group, but this is an outer surface protective cover glass. Two parallel flat plates are arranged between the fourth lens group and the image. These are an infrared cut filter and an image sensor cover glass in this order from the endoscope side. The entrance pupil position is the distance from the first surface (the endoscope side surface of the outer protective cover glass) toward the image side.

Further, in the sectional views of the respective embodiments, FIG.
2B shows the wide end, FIG. 2C shows the telephoto end, FIG. 2A to FIG.
(B) shows the telephoto end.

In FIGS. 6 to 10, the horizontal axis represents the logarithm of the focal length, and the vertical axis represents the distance from the most image side surface of the first lens unit G1. 11 to 15, the horizontal axis is the logarithm of the focal length, and the vertical axis is the magnification.

As described above, according to the present invention, in addition to the first, second, and third aspects of the present invention, the optical systems described in the following aspects can also achieve the object.

(1) In the optical system described in claims 1, 2 or 3, the paraxial lateral magnification of the second lens group and the third lens group is substantially -1 simultaneously within the zooming range. A zoom imaging optical system for an endoscope, characterized by including a state.

(2) The optical system according to claim 1, 2, or 3 or (1), wherein
The lens group includes one positive lens and one negative lens having an Abbe number smaller than the positive lens, and the second lens group includes a positive lens and one negative lens having a lower refractive index and a lower dispersion than the positive lens. A cemented lens having a cemented surface having a positive refractive power;
The lens group includes three or more lens components, and at least one of the lens components of the third lens group includes a negative lens made of a material having an Abbe number of 40 or less. At least one lens component of the lens components is a cemented lens component having a cemented surface having a negative refractive power.

(3) The optical system according to claim 1, 2, or 3, or the optical system according to (1) or (2),
A zoom imaging optical system for an endoscope, which satisfies the following conditions (5), (6), (7), and (8). (5) n _2P > 1.7 (6) 0.03 <n _2P −n _2N <0.15 (7) ν _2P <35 (8) ν _2N −ν _2P > 15

(4) The optical system according to claim 1, 2, or 3, or (1), (2), or (3), wherein the fourth lens group has a paraxial horizontal axis. A zoom imaging optical system for an endoscope, wherein a magnification is always less than 1.

[0101]

According to the present invention, there is provided an endoscope zoom optical system which can be used even when the zoom ratio exceeds 2, and a zoom imaging optical system which is suitable for forming a rigid endoscope visual field conversion system by cutting out an optical image. System can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the present invention.

FIG. 5 is a sectional view of a fifth embodiment of the present invention.

FIG. 6 is a diagram illustrating the movement trajectories of the second and third lens groups according to the first embodiment of the present invention.

FIG. 7 is a diagram illustrating the movement trajectories of the second and third lens units according to the second embodiment of the present invention.

FIG. 8 is a diagram showing the movement locus of the second and third lens groups according to the third embodiment of the present invention.

FIG. 9 is a diagram showing the movement trajectories of the second and third lens groups according to a fourth embodiment of the present invention.

FIG. 10 is a diagram showing the movement trajectories of the second and third lens units according to a fifth embodiment of the present invention.

FIG. 11 is a diagram showing a magnification change of the second and third lens units according to the first embodiment of the present invention.

FIG. 12 is a diagram showing a magnification change of the second and third lens units according to the second embodiment of the present invention.

FIG. 13 is a diagram showing a magnification change of the second and third lens units according to the third embodiment of the present invention.

FIG. 14 is a diagram showing a magnification change change of the second and third lens units according to the fourth embodiment of the present invention.

FIG. 15 is a diagram showing a magnification change of the second and third lens units according to Example 5 of the present invention.

FIG. 16 is an aberration curve diagram at the wide-angle end according to the first embodiment of the present invention.

FIG. 17 is an aberration curve diagram at the intermediate focal length according to the first embodiment of the present invention.

FIG. 18 is an aberration curve diagram at the telephoto end according to the first embodiment of the present invention.

FIG. 19 is a diagram showing a basic configuration of an imaging device connected to a rigid endoscope;

FIG. 20 is a diagram showing a configuration of a visual field conversion imaging device connected to a rigid endoscope;

FIG. 21 is a diagram showing the concept of field of view conversion.

Claims (3)

[Claims] An imaging optical system connected to an eyepiece of an endoscope, wherein a positive lens for focusing by moving a lens group or a part of lenses in the lens group in the optical axis direction in order from the endoscope side. A first lens group with a focal length, a second lens group with a negative focal length that moves in the optical axis direction during zooming, a third lens group with a positive focal length that moves in the optical axis direction during zooming, and It consists of a fixed fourth lens group, and has the following conditions (1), (2),
A zoom imaging optical system for an endoscope, which satisfies (3). (1) 0.3 <β ₄ <3 (2) −1.2 <f ₂ / f _W <−0.5 (3) −1.3 <f ₂ / f ₃ <−0.5 where β ₄ is the focal length of the fourth paraxial lateral magnification of the lens group, f _W is the total focal length at the wide end, f _2, f ₃ are each second and third lens groups. 2. The zoom imaging optical system for an endoscope according to claim 1, wherein the following condition (4) is satisfied. (4) 0.7 <β _2W / β _3W <1.4 where β _2W and β _3W are paraxial lateral magnifications of the second lens unit and the third lens unit, respectively, at the wide ends. 3. An imaging optical system connected to an endoscope eyepiece, wherein a positive lens for focusing by moving a lens group or a part of lenses in the lens group in the optical axis direction in order from the endoscope. A first lens group with a focal length, a second lens group with a negative focal length that moves in the optical axis direction during zooming, a third lens group with a positive focal length that moves in the optical axis direction during zooming, and A zoom optical system including a fixed fourth lens group, and a solid-state image sensor unit movable in a direction perpendicular to the optical axis in order to move the field of view of the endoscope.
A zoom imaging optical system for an endoscope, which satisfies (2) and (3). (1) 0.3 <β ₄ <3 (2) −1.2 <f ₂ / f _W <−0.5 (3) −1.3 <f ₂ / f ₃ <−0.5 where β ₄ is the focal length of the fourth paraxial lateral magnification of the lens group, f _W is the total focal length at the wide end, f _2, f ₃ are each second and third lens groups.