JPH0820613B2 - Endoscope optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an endoscope optical system using a heterogeneous medium lens, whose refractive index decreases from the central portion to the outer peripheral side, as a relay lens, and in particular, a hard lens. Mirror optics.

[Conventional example]

FIG. 7 shows an example of this type of endoscope optical system,
Reference numeral ₁ denotes an objective lens which is configured by arranging two plano-convex lenses with their convex surfaces facing each other and forms an image M _{1 of the} object M on its exit surface or in the vicinity thereof. The exit surface has a length kP (where P is the pitch of the inhomogeneous medium,
There is a relay action or imaging action twice in 1P. Further, k is a positive integer. ) The non-homogeneous medium relay lens 2 is joined to prevent the dust and the like from adhering to the exit end face of the non-homogeneous medium relay lens, and the object image M ₂ and dust formed on the exit end face at the same time. A cover glass 3 for preventing the visibility is joined. On the rear side of the cover glass 3, a one-time relay lens for reversing and erecting the object image M ₂ by the inhomogeneous medium relay lens 2 and for correcting magnification and axial chromatic aberration generated in the inhomogeneous medium relay lens 2 4 and
The aperture stop 5 is arranged once at the pupil position of the relay lens 4 to adjust the depth of field and uniformize the brightness within the field of view, and to reduce flare, and is arranged behind the relay lens 4. a field lens 6 for adjusting the position and the magnification of the eye point E _X P Te, once the relay lens 4 and the field stop 7 arranged at an imaging position of the image M ₃ by the field lens 6, the rear side of the field stop 7 And the cover glass 9 arranged on the rear side of the eyepiece lens 8, which magnifies the image M ₃ regulated by the field stop 7.

As another one of the conventional endoscope optical systems of this type, for example, the one disclosed in Japanese Utility Model Laid-Open No. 55-147013 has a length of mp / 2 (however, as shown in FIG. 8). m is a positive integer)
A slightly different inhomogeneous medium lens 10 is used, and the image M ₂ transmitted thereby is imaged before or after the exit end face of the inhomogeneous medium lens 10 so that dust adhering to the exit end face can be seen together with the image. This is different from the above-described conventional example in that the relay lens 4 and the field lens 6 are not necessary once.

[Problems to be Solved by the Invention]

However, the one shown in FIG. 7 has a problem that the manufacturing cost is high because the relay lens 4 has a two-group configuration and is expensive. Further, the one shown in FIG. 8 is advantageous in terms of cost because it does not have the relay lens 4, but the image deterioration is remarkable because there is no optical system for correcting the chromatic aberration generated in the heterogeneous medium relay lens 10. There was a problem. Also, since there is no position for placing the aperture stop on the rear side of the heterogeneous medium relay lens 10, it may be possible to provide it on the objective lens 1 side, that is, at the point A in FIG. 8, but the outer diameter of the objective lens 1 is at most 1 mm. Therefore, it was extremely difficult to provide a donut-shaped diaphragm within this diameter in terms of the accuracy and processing of parts. Further, the field stop 7 has no place when the image M ₂ is formed in the inhomogeneous medium relay lens 10, and if it is placed on the exit end face of the inhomogeneous medium relay lens 10, the image M ₂ and the field stop 7 are not provided. There was a problem that the inner diameter portion of 7, that is, the mask was out of focus at the same time, and it was difficult to see. Furthermore, when the endoscope is made side-view type,
There is also a problem in that there is no position on the rear side of the heterogeneous medium relay lens 10 for placing an image rotator for making a back image by the reflecting prism in the objective lens a front image.

In view of the above problems, it is an object of the present invention to provide an endoscope optical system that has a low manufacturing cost and can obtain a good observation image.

[Means and Actions for Solving the Problem] The endoscope optical system according to the present invention is an endoscope optical system in which a heterogeneous medium lens whose refractive index decreases from the central portion toward the outer peripheral side is used as a relay lens. In the system, when the length from the incident image forming position of the inhomogeneous medium lens to the exit end face is L, the following condition is satisfied.

(2) 0.15 <C <0.35 where n is 0 or a positive integer, and P is the pitch (cycle).

The following effects can be obtained by adopting the above configuration.

(A) The length of the inhomogeneous medium lens required for n imaging operations And CP, which is shorter than the length required for one imaging operation, and CP is a length within a predetermined range centered on 1/4 P. As a result, the exit end face of the inhomogeneous medium lens is largely separated from the relayed image position, and even if a considerable amount of dust adheres to the end face, it does not interfere with the image observation.

(B) When the object image is arranged on the entrance end surface of the inhomogeneous medium lens, a brightness diaphragm can be provided at or near the exit end surface, and its position is the holding portion of the endoscope, that is, Since it is a large diameter part, the outer diameter of the aperture diaphragm can be made large, and since the focal length of the lens system after the exit end surface is longer than that of the objective lens, the inner diameter of the aperture diaphragm can be made large if the numerical aperture is the same. Therefore, it is easy to provide a brightness diaphragm in terms of accuracy and processing of parts.

(C) When arranged so that an object image is formed on the entrance end surface of the inhomogeneous medium lens, the exit end surface or its vicinity is the pupil position, so a 1 / 2-time relay lens (0.25P relay lens) Is required, and by using an achromatic doublet lens composed of a glass lens, it is possible to correct the magnification and axial chromatic aberration generated in the inhomogeneous medium lens.

(D) Since an image is formed outside the inhomogeneous medium lens, a field stop can be arranged there, and as a result, the image and the inner diameter portion of the field stop are in focus at the same time, and are easy to see.

(E) Since the image rotator can be placed on the rear side of the inhomogeneous medium lens even when the endoscope is a side-view type, a surface image can be obtained.

〔Example〕

The present invention will be described in detail below with reference to the same members as those of the above-described conventional example based on the illustrated embodiments.

FIG. 1 shows the first embodiment, and 11 is the objective lens 1.
Joined to Is a non-homogeneous medium relay lens having a length of, and an image M ₁ formed by the objective lens ₁ is formed on the incident end surface of the relay lens 11 or in the vicinity thereof, and the exit end surface or the vicinity thereof is the pupil position. Reference numeral 12 denotes a cover glass having the front surface to which the aperture stop 5 is attached or vapor-deposited and which is joined to the exit end surface of the heterogeneous medium relay lens 11, and 13 denotes a glass lens or the like arranged on the rear side of the cover glass 12. It is a 1/2 time relay lens.

This embodiment is configured as described above, the exit end surface of the heterogeneous medium relay lens 11 or its vicinity is the pupil position,
No image is formed here, so no dust can be seen with the image even without the cover glass. When the length of the heterogeneous medium relay lens 11 is L, the range is (However, n can be 0 or a positive integer), but if it deviates from this, dust will be seen with the image.

Further, since the aperture stop 5 is located on the exit end surface of the heterogeneous medium relay lens 11, and this position is the holding portion of the endoscope, that is, the large diameter portion, the outside diameter of the aperture stop 5 can be made large.
The numerical apertures of the objective lens 1 and the 1/2 times relay lens 13 are the same, but the focal length of the 1/2 times relay lens 13 is much longer, so that the inner diameter of the aperture stop 5 can be made large. Therefore,
Providing the aperture stop 5 is easy in terms of accuracy and processing of parts. Further, since the aperture stop 5 is formed on the cover glass 12, there is an advantage that it can be made thin.

Further, the 1/2 times relay lens 13 is required, and by making it an achromatic doublet lens, it is possible to correct the magnification and the axial chromatic aberration generated in the heterogeneous medium relay lens 11.

Further, an image M ₂ is formed outside the inhomogeneous medium relay lens 11, and the field stop 7 is arranged there, so that the image M ₂ and the inner diameter portion of the field stop 7 are in focus at the same time and are easy to see.

Therefore, a good observation image can be obtained from the above results.
Further, since the relay lens 13 has a one-group configuration and is inexpensive, the manufacturing cost is also reduced.

FIG. 2 shows a second embodiment, in which the aperture stop 5 is not formed on the cover glass but is independently attached to the exit end face of the heterogeneous medium relay lens 11.

FIG. 3 shows a third embodiment in which an image rotator 14 is arranged between the cover glass 12 and the 1 / 2-time relay lens 13 so that the back image by the reflecting prism 1a in the objective lens 1 is formed. It is made to be an image. The image rotator 14 is not necessary when the reflecting prism 1a is a roof prism.

FIG. 4 shows a fourth embodiment, in which a plurality of inhomogeneous relay lenses 11, for example, three inhomogeneous medium lenses 11 ₁ and 11 are used.
_2, 11 ₃ constituted by joining the image position or the vicinity thereof, and the last inhomogeneous medium lenses 11 ₃ the length L ₃ And the lengths L ₁ and L ₂ of the other inhomogeneous medium lenses 11 ₁ and 11 ₂ are set to L ₁ and L ₂ = nP / 2. Since we are image formed by the objective lens is formed on the incident end face of the inhomogeneous medium lenses 11 _1, the sum of the lengths of the three inhomogeneous medium lenses
L ₁ + L ₂ + L ₃ corresponds to L in the claims. Therefore,
In this embodiment, a plurality of short inhomogeneous medium lenses, which are technically easier and cheaper to manufacture than a long inhomogeneous medium lens, are used. Therefore, the manufacturing is easy and the cost is low.

FIG. 5 shows a fifth embodiment, which is a photographing lens.
A solid-state image sensor 17 via a shooting adapter 16 with a built-in 15.
In this case, a TV camera head 18 having a built-in lens is attached, and in this case, the image forming position by the taking lens 15 coincides with the image pickup surface of the solid-state image pickup device 17.

FIG. 6 shows a sixth embodiment in which the eyepiece lens portion is removed and the TV camera head 18 is attached. In this case, the image formation position by the 1/2 times relay lens 13 is solid-state imaging. The image pickup surface coincides with the image pickup surface of the element 17, and the image pickup surface also serves as a field stop.

〔The invention's effect〕

As described above, the endoscope optical system according to the present invention is low in cost, prevents dust attached to the exit end surface of the inhomogeneous medium lens from interfering with observation, and has high component accuracy required for the aperture stop. And eliminate the difficulty in processing,
Furthermore, it is possible to correct the magnification and axial chromatic aberration generated by the inhomogeneous medium lens.

[Brief description of drawings]

FIG. 1 is a view showing a first embodiment of an endoscope optical system according to the present invention, FIGS. 2 to 6 are views showing second to sixth embodiments, respectively, and FIGS. 7 and 8 are respectively. It is a figure which shows a prior art example and other prior art examples. 1 ... Objective lens, 5 ... Brightness diaphragm, 7 ... Field diaphragm, 8 ... Eyepiece lens, 9,12 ... Cover glass, 11 ......
Heterogeneous medium relay lens, 13 ... 1/2 times relay lens, 1
4 …… image rotator, 15 …… shooting lens, 16…
… Shooting adapter, 17 …… TV camera head, 18 …… Solid-state image sensor.

Claims (2)

[Claims] 1. An endoscope optical system comprising an objective lens and a relay lens composed of a heterogeneous medium lens whose refractive index decreases from the central portion toward the outer peripheral side, wherein an exit end surface of the relay lens or An aperture stop is arranged in the vicinity of the relay lens, and an image forming lens for forming an image by receiving light emitted from the relay lens is provided on the rear side of the exit end surface of the relay lens. An endoscope optical system, wherein the following condition is satisfied, where L is the distance to the exit end face of the inhomogeneous medium lens. L = [(n / 2) + C] P 0.15 <C <0.35 However, n is 0 or a positive integer, P is a pitch (cycle). 2. The endoscope optical system according to claim 1, wherein the focal length of the imaging lens is longer than the focal length of the objective lens.