JPS604963B2 - endoscope objective lens - Google Patents

Description

[Detailed description of the invention] The present invention relates to an endoscope objective lens.

An endoscope has an extremely small outer diameter, and various functions such as an observation optical system and an illumination optical system must be built into the endoscope.

For this reason, each endoscope objective lens is required to have a very small diameter. Furthermore, in an endoscope that uses an image fiber handle in the image transmission optical system, light rays that enter the end face of the image fiber at a large angle of incidence are not transmitted.
For this reason, it is desirable that the light incident on the end face of the image fiber be as close to parallel to the optical axis as possible. The present invention provides an extremely compact and wide-angle endoscope objective lens that satisfies these requirements.

The details of this competition will be explained below.

The present invention includes, in order from the object side, a front group diverging lens system consisting of a lens having negative refractive power, and a positive varnish lens system in which the absolute value of the radius of curvature of the surface on the object side is larger than the absolute value of the radius of curvature of the rear surface. It is a retrofocus lens system consisting of a rear group converging lens system consisting of a cemented lens having a cemented surface having a negative refractive power, and a rear group converging lens system consisting of the above-mentioned front group diverging lens system and rear group converging lens system. This is a compact, wide-angle endoscope objective lens that is capable of shortening the overall length of the lens system by reducing the distance between the front group and the outer diameter of the front group diverging lens system. The lenses constituting the front group diverging lens system have object-side surfaces that are flat or convex so that they also serve as a cover glass. Furthermore, by arranging an aperture stop in front of the first lens of the rear group converging/emitting lens system or on the object side surface of the first lens, the angle of incidence of the light rays entering the end face of the image fiber is made as close to perpendicular as possible. , This makes it possible to improve the angular characteristics of the image fiber's transmittance. Generally, in a retrofocus type objective lens, the curvature of the bride surface can be corrected over a wide image plane, but spherical aberration and chromatic aberration of magnification deteriorate. Therefore, in the present invention, the correct lens on the object side of the rear group focusing lens system is configured such that the absolute value of the radius of curvature of the surface on the object side is larger than the absolute value of the radius of curvature of the surface on the image side. This, combined with the fact that the cemented surface of the positive cemented lens in the rear group aperture lens system has negative refractive power, corrects spherical aberration and chromatic aberration of magnification. In addition to such a lens configuration, the objective lens of the present invention is characterized by satisfying the following conditions. '1
) 1.0SmSI. 38 {2}o-7milf {te ten (roux 1) precious}1≦1-2 skin・5≦f point・≦・. 5 However, " m is the composite of the entire system. The ratio of the composite focal length of the rear group to the focal length, f is the composite focal length of the entire system, and L' is the focal length of the front group. "The ratio is the ratio of the composite focal length of the rear group to the focal length. The refractive index of the lens, ro is the radius of curvature of the first surface of the rear group, r
a is the radius of curvature of the joint surface of the joint lens in the rear group.

To describe each condition in the objective lens of the present invention explained above, if m exceeds the upper limit in condition '1, the conjugate distance of the rear group convergence lens system increases in proportion to the focal length, so the objective lens The total length of the lens becomes longer, and when this lens is used in an endoscope, the rigid tip becomes longer, which is undesirable because it causes pain to the patient.

Moreover, when the lower limit is exceeded, the height of incidence on the rear group converging lens system is constant, and the composition of the rear group converging lens system. When the focal length becomes small, the angle of view to the rear group aggregation lens system increases, which deteriorates the field curvature, making it impossible to use it as an endoscope objective lens. Next, conditions (2) and (3)' are conditions for satisfactorily correcting astigmatism in the meridional direction while simultaneously correcting the symmetry of comatic aberration. Among these conditions, condition '2} has the largest effect of correcting the off-axis spherical aberration on the lower ray, and the degree of the correction effect differs in the order of the lower ray, the chief ray, and the upper ray. In contrast, in the conditional lake, the degree of correction is different in the order of upper ray, chief ray, and lower ray, and the off-axis spherical aberration correction effect on the upper ray is the largest. These conditions ■ and conditions {31
If the upper limit of is exceeded, astigmatism can be corrected, but the symmetry of comatic aberration cannot be corrected satisfactorily. That is, condition '21
If exceeds the upper limit, the lower ray of spherical aberration outside the sea bream will be over-corrected, and the upper ray will be under-corrected. On the other hand, if condition '3' exceeds the upper limit, the lower ray of the extra-marginal spherical aberration will be under-corrected and the upper ray will be over-corrected. Furthermore, if the lower limit of the conditions {2- and t3} is exceeded, astigmatism in the meridional direction will be insufficiently corrected. If one of these conditions ■ and {3} exceeds the lower limit, the astigmatism in the meridional direction can be corrected by increasing the other one to a large value close to the upper limit, but this method For the reasons mentioned above, the symmetry of the coma deteriorates, making it impossible to use it as an endoscope objective lens. Next, an example of the endoscope objective lens according to the present invention described above will be shown.

Example 1 d of rl=: 0.37n, 1.51633 〃, ni. 15
r2=1.13Q=0.36 r3=-2.294 Rakko0.60n2=1.757 R2=47.87r
4 = -0.816q = 0.20 r5i's = 0.35n3 = 1.84666 Re3 Ko23. Total r6=1.13chi=0.61n4=1.7separation 4:4
7.49r7=-1.564f=・, Skin Melon Agency.

．． Carrying in fzu(〜-・)三}=-.

-789R=3-6 Example 2 r・E13.908 d,=0.32n,D1.516 killed,=64.15
r2=2.111 et al=0.92 r3=-1.366 et al=0.69n2=1.757 re2=47.87r
4=-1.042Q=0.09 r5=3.688 Home=0.32n3=1.84666 y3=23.8
8r6=0. Skin Q = 0.78n4 = 1.7 Iso 〃4
=47.49r? =-1.831f=1・m=1・11
0 city i = skin, f {number + (~-・)sa} = -.

76 or more R = 43 In the above example, r,, r2,... are the radius of curvature of each lens surface, d,,... are the gap between each lens surface, n,, n2, ... is the refractive index of each lens〃,, ri2
, ... is the Abbe number of each lens, f is the composite focal length of the entire system, m is the ratio of the composite focal length of the rear group yield lens system to the composite focal length of the entire system, and f is the front In the diverging lens system, ~ is the refractive index of the first lens of the rear group convergence lens system, ro is the radius of curvature of the first surface of the rear group convergence lens system, and ra is the cementation of the rear group convergence lens system. Radius of curvature of the cemented surface of the lens, R
This is the distance from the apex of the first surface of the solar system to the rear focal point.

Further, in each example, the ratio is n2, ra is r3, and ra is r6. The diamond collection situation of each example is shown in FIGS. 3 and 4, respectively. In addition, in the present invention, regardless of the method of extending the entire objective lens during focusing,
A method can be adopted in which the rear group is moved to change the lens distance between the front group and the rear group.

Therefore, a cover glass can be used for both the front group and the front group without using a special cover glass, which is useful for downsizing the rigid tip portion of the endoscope near the objective lens. As explained above, according to the present invention, it is possible to provide an extremely compact endoscope objective lens, which is extremely suitable for an endoscope that is thinner and has a short rigid tip portion.

[Brief explanation of drawings]

1 and 2 are sectional views of each embodiment of the endoscope objective lens of the present invention, and FIGS. 3 and 4 are aberration curve diagrams of each embodiment, respectively. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. A front group diverging lens system consisting of a lens having negative refractive power, and a positive meniscus lens in which the absolute value of the radius of curvature of the surface on the object side is larger than the absolute value of the radius of curvature of the surface on the image side. A retrofocus lens system consisting of a cemented positive lens whose cemented surface has a negative refractive power and a rear group convergent lens system,
An endoscope objective lens characterized by satisfying each of the following conditions. (1) 1.0≦m≦1.38 (2) 0.7≦｜f(1/
(f_1)+(n_0-1)1/(r_0))|≦1.
2 (3) 0.5≦f1/(|r_a|)≦1.5, where m is the ratio of the composite focal length of the rear group convergent lens system to the composite focal length of the entire system, and f_1 is the ratio of the composite focal length of the rear group convergent lens system to the composite focal length of the entire system. The focal length, f is the combined focal length of the entire system, n_0 is the refractive index of the first lens of the rear group convergent lens system, r_0 is the radius of curvature of the first surface of the rear group convergent lens system, and r_a is the radius of curvature of the first surface of the rear group convergent lens system. This is the radius of curvature of the cemented surface of a cemented lens.