JPH02188709A - Objective lens for endoscope - Google Patents

Abstract

PURPOSE:To compensate an on-axis chromatic aberration and a magnification chromatic aberration with good balance by composing the objective of a 1st negative lens, and a 4th cemented lens which has a negative refractive index on the whole in order from the object side and satisfying specific conditions. CONSTITUTION:The objective consists of the 1st negative lens L1, the 2nd positive lens L2, the 3rd positive lens L3, and the 4th cemented lens L4+L5 which has the positive refracting power on the whole in order from the object side. Then, a brightness stop is arranged between the 2nd lens L2 and 3rd lens L3 and the conditions shown by inequalities I, II, III, and IV are satisfied. In the inequalities I-IV, f1 is the focal length of the 1st lens, (f) the composite focal length of the whole system, n2, n3, and n4 the refractive indexes of glass materials used for the 2nd lens, 3rd lens, and 4th cemented lens. Further, nu2, nu3, nu4, and nu5 are the Abbe numbers of the glass materials used for the 4th cemented lens L4+L5, and the concave lens L5 of the 4th cemented lens. Consequently, the on-axis chromatic aberration and magnification chromatic aberration are compensated excellently with good balance.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to an objective lens for an endoscope used in a small diameter endoscope with a small outer diameter, and in particular, C8C, D, and C8C as imaging elements.
The present invention relates to an objective lens for an endoscope using a (Charge Coupled Device).

[Conventional technology]

In recent years, with the increasing demand for smaller diameter endoscopes such as bronchoscopes that are inserted into narrow lumens such as bronchi for observation and treatment, we have developed new products for endoscopes with small outer diameters used for these purposes. Various objective lenses have been developed. In this type of objective lens for an endoscope, as a lens system similar to the objective lens for an endoscope according to the present invention, as shown in FIG. a plano-concave negative second lens Lt' that faces toward the object side, a biconvex positive second lens Lt' whose surface with a large radius of curvature faces the object side, and a third lens that has a positive refractive index as a whole.
It consists of a cemented lens L;+L; and a fourth meniscus lens L5' with its convex surface facing the image side, and the second lens Lt''
This is an objective lens for an endoscope in which an aperture A is arranged between the third cemented lens L; radius of curvature d of lens surface
+,'d3,...d,: Thickness or air spacing of each lens nl, n3, nx, n4, ns: Refractive index of each lens for the d-line ν1·shi3, sh3. C4. ν5: When it is the Atsube number of each lens, m r d n ν1
ω 2 0.502 0.281 1.8B300
41.03 1.406 0.176 4 -0.879 0.949 1.72916
54.85 7.032 0.211 6 -0.586 1.020 1.72916
54.87 -1.082 0.281 1.805
18 25.58 -0.582 0.295 9 -1.803 0.2B1 1.80518
25.5, there is an objective lens for an endoscope that has an aberration curve diagram as shown in FIG.

[Problem to be solved by the invention]

However, in lens systems using cemented lenses such as those mentioned above, chromatic aberration is corrected by reducing the radius of curvature of the cemented surface of the cemented lens. In addition to having limitations in terms of machining, polishing and processing the lens becomes extremely difficult when reducing the radius of curvature.

If this chromatic aberration is not sufficiently corrected, it will hinder accurate observation and accurate diagnosis when observing and diagnosing the inside of the lumen using an endoscope.

In view of the current situation, the present invention provides an objective lens for an endoscope in which longitudinal chromatic aberration and lateral chromatic aberration are corrected well in a well-balanced manner by arranging a convex lens made of a glass material with large dispersion in front of the diaphragm. The purpose is to

[Means for Solving the Problems and Their Effects] In order to achieve the above object, the present invention provides a negative second lens Lz in which the concave surface is directed from the object side toward the image side, and a surface with a large radius of curvature is directed toward the image side. The second lens L2 is composed of a positive second lens L2 that faces toward the object side, a third positive lens L1 that has a surface with a large radius of curvature facing the object side, and a fourth cemented lens L4+Ls that has a positive refractive index as a whole. In an objective lens for an endoscope in which an aperture stop is arranged between the lens L2 and the third lens L3, (1) 0.
60<l f+/rl<0.70(2) n
z >1.60 12< 45.0(3) n3>
1.60 vz > 50.0 (4L na >
1.60 va > 50.0 (5) ν5 < 4
0.0 Where, fl: Focal length of the first lens f: Combined focal length of the entire system n3, n3, n4, ? The refractive index ν3, ν3 . .
ν4. ν5: second lens L3, third lens L3. Fourth
Convex lens L4 of cemented lens L4+L5. In an endoscope objective lens characterized by satisfying the condition of the Atsube number of the glass material used in the concave lens L5 of the fourth cemented lens l-a + Ls, and similar lenses, formula (4) and ( 5) This is an objective lens for an endoscope in which only the formula is changed as follows.

(4) ν4<40.0 (5) ns >1.60 vs > 50.
0 However, ns: refractive index ν4 for the d-line of the glass material used for the convex lens L5 of the fourth cemented lens t, 4+L5. ν5
: fourth cemented lens L4+L, concave lens L4. The significance of the above-mentioned conditions below will be explained below with respect to the Atsube number of the glass material used for the convex lens L5 of the fourth cemented lens LA+L5.

First, condition (1) defines the power of the first lens Ll, and if the upper limit is exceeded, the focal length of the first lens Ll becomes longer, so the power of the first lens Ll becomes longer than the upper limit. On the other hand, if the lower limit is not satisfied, the radius of curvature of the concave surface of the first lens Ll becomes small, making it difficult to polish and process the lens.

Conditions (2) to 5) are satisfied when the first lens L1.
This limits the glass materials that should be used for the convex and concave lenses of the second lens L3, third lens L3, and fourth cemented lens L a + L s. If the refractive index of the convex lenses is less than this, the Petzval sum deteriorates. , the correction of field curvature becomes insufficient, and furthermore, in order to obtain the same lens power without satisfying this condition, the radius of curvature must be made smaller, making polishing and processing of the lens difficult. Furthermore, if the Abbe number of each glass material falls outside of this range, it becomes difficult to achieve a well-balanced correction of longitudinal chromatic aberration and lateral chromatic aberration, which is the original objective of the present invention.

Note that by making the objective lens for an endoscope have the lens configuration of the present invention, the first lens Ll and the fourth cemented lens Ln+L
The outer diameter ratio of s is 1. Since it is possible to make the lens close to O, it is possible to reduce the outer diameter of the entire objective lens for an endoscope.

Furthermore, since C, C, O, etc. are used as imaging elements at the imaging position P of the lens configuration of the present invention, there is no need to configure the objective lens in a telecentric system.

〔Example〕

Hereinafter, each embodiment of the present invention will be described in detail based on the drawings.

However, in the following explanation, L, to L5: 1st lens to 5th lens radius d
,, d,,...dl: Thickness or air spacing of each lens nl, n3, n3, n4, ns: Refractive index of each lens for the d-line, ν2, ν3, ν4, νS: Atsube number of each lens shall be. Note 5. The optical path in the diagrams for each lens configuration represents the principal ray at an object height of 601 under the same conditions, and each aberration curve diagram represents the principal ray at an object height of 20, 40, and 60 when the subject distance is 5 cm and the effective F number is 5.60. Indicates the amount of aberration.

The first embodiment is based on the basic first lens configuration shown in FIG. 1, and is as shown in the table below.

m r d
n νl c.

2 0.51 0.32B 1.81550
44.43 1.125 0.131 4 ω 0.7B7 1.70154 4
1.15 (X) 0.020 6 -0.846 0.656 1.62280
56.97 1.928 0.066 8 -0.794 0.852 1.62280
56.99 -11.705 0.32B 1
．． 80518 25.5f=1 r, −-0,625 I f , /f I =0.625 and hF: Height of chief ray at initial maximum angle of view of first lens L1 h: 441st! In this example, when the height of the principal ray at the maximum angle of view of the final surface of the cemented lens La +L5 is h, =0.4
34 hll=0.424, and hr/h@I=1.024.

The aberration curve with this specific configuration is as shown in FIG.

The second embodiment is based on the basic first lens configuration shown in FIG. 1, and its specific configuration is as shown in the table below.

m r d n ν1
o.

2 0.545 0.280 1.81550
44.43 1275 0.140 4 ω 0.771 1.70154 4
1.15 ω 0.042 6 -0.904 0.631 1.72000
50.37 3.523 0.070 8 -0.701 0.841 1.72000
50.39 -13, 541 0.280 1
．． 80518 25.5f = 1 f+ = -0,669 r +/f I = 0.669 and hF: Height of chief ray at initial maximum angle of view of first lens L1 hl: Final height of #4 cemented lens LA+L5 In this example, when the height of the chief ray at the maximum angle of view of the surface is hv = 0.4.
21 h true = 0.408, and hr/h arm 1 = 1.032.

The aberration curve according to this specific configuration is as shown in FIG.

Furthermore, the third embodiment is based on the basic first lens configuration shown in FIG. 1, and its specific configuration is as shown in the table below.

m r d
n ν1 o.

2 (L545 0.280 1.81
550 44.43 1.251 0.14
0 4 31.630 0.771 1.723
42 38.05 -24.696 0.04
26 -0.875 0.631 1.72
000 50t37 3.527 0.07
0 8 -0.701 0.841 1.720
00 50.39 -13, 533 0.280
1.8051B 25.5f = 1 f, = -0,668 1f I/fl = 0.668 and hF: height of chief ray at initial maximum angle of view of first lens L, hl: 41st # junction In this example, when the height of the chief ray at the maximum angle of view of the final surface of lens L4 + L5 is hF = 0.4.
21 ha = 0.410, and hF/ ha = 1.02''?

The aberration curve with this specific configuration is as shown in FIG.

Furthermore, the fourth embodiment is based on the basic second lens configuration shown in FIG. 2, and its specific configuration is as shown in the table below.

m r d n ν1
8.000 2 0.500 0.280 1.81550
44.43 0.951 0.140 4 3,000 0.771 1.72825
2B, 35 1.429 0.042 6 -0.916 0.631 1.69680
55.67 -56.693 0.070 8 1.272 0.280 1.80518
25.59 -3, 745 0.841 1.6
9680 55.6f = 1 f, =, -0,665 r, /f l =0.665 and hF: Height of the chief ray at the maximum angle of view of the first lens and the cross section hll: Fourth cemented lens In this example, when the height of the principal ray at the maximum angle of view of the final surface of L a + L s is hr = 0.4
51 h feces = 0.483, and br/h proverb -0,934.

The aberration curve with this specific configuration is as shown in FIG.

A third aberration curve diagram of each of the first to fourth embodiments described above.
．． The chromatic aberration of magnification in FIGS. 4 and 5.6 has been corrected to about half or less of the chromatic aberration of magnification in FIG. 8, which is an aberration curve diagram of the conventional example.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the lens configuration and conditions (1) to (5) are satisfied, so that the objective lens for an endoscope has wide angle of view characteristics. In addition, various aberrations based on monochromatic light and chromatic aberration of magnification can be well corrected to improve resolution, making it possible to provide an objective lens for endoscopes with improved observation and diagnostic functions. .

Furthermore, it has become possible to provide an objective lens for an endoscope that is easy to polish and process.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of the basic second lens configuration of the present invention, FIG. 2 is a lens configuration diagram of the basic second lens configuration, and FIG.
The figure is an aberration curve diagram of the first embodiment, FIG. 4 is an aberration curve diagram of the second embodiment, FIG. 5 is an aberration curve diagram of the third embodiment, and FIG. 6 is an aberration curve diagram of the fourth embodiment. FIG. 7 is a conventional lens configuration diagram, and FIG. 8 is an aberration curve diagram corresponding to FIG. 7. Ll to Ls: 1st lens to 5th lens
't,...d,: Thickness or air distance P of each lens:
Imaging position patent applicant Fuji Photo Koki Co., Ltd. Tamaki 1 left Fig. 3 4 ω 3? @Llf outside Figure 6 Itin 噌蓼- fEIIBLllyL Kai 11〼音 4 禮 4?゜4゜ Display of the case 1999 Patent Application No. 7828 Name of the invention Person who corrects objective lenses for endoscopes Relationship to the case Patent applicant address 1-324 Uetake-cho, Omiya City, Saitama Name (5)
43) Fuji Photo Kohki Co., Ltd. Representative Minoru Mori 105 Telephone 501-4552 Address 4F Shimazaki Building, 1-2-14 Toranomon, Minato-ku, Tokyo 5°6°7° This is a voluntary correction of the date of the correction order. This is the [Detailed Description of the Invention J] Contents of Amendment column in the subject specification.

Claims (1)

[Claims] (1) In order from the object side, a negative first lens L_1 with a concave surface facing the image side, a positive second lens L_2 with a surface with a large radius of curvature facing the image side, and a radius of curvature. The second lens consists of a positive third lens L_3 whose large surface faces the object side, and a fourth cemented lens L_4+L_5 which has positive refractive power as a whole.
In an objective lens for an endoscope with an aperture diaphragm placed between lens L_2 and third lens L_3, (1) 0.60<|f_1/f|<0.70(2) n_
2>1.60 ν_2<45.0(3)n_3>1.6
0 ν_3>50.0(4)n_4>1.60 ν_4
>50.0 (5) ν_5<40.0 However, f_1: Focal length of the first lens f: Combined focal length of the entire system n_2, n_3, n_4: Second lens L_2, third lens L_3, fourth cemented lens Convex lens L of L_4+L_5
Refractive index for the d-line of the glass material used in _4 ν_2, ν_3, ν_4, ν_5: second lens L_2,
An objective lens for an endoscope, characterized in that it satisfies the condition of the number of glass materials used for the third lens L_3, the convex lens L_4 of the fourth cemented lens L_4+L_5, and the concave lens L_5 of the fourth cemented lens L_4+L_5. (2) In order from the object side, a negative first lens L_1 with a concave surface facing the image side, a positive second lens L_2 with a surface with a large radius of curvature facing the image side, and a surface with a large radius of curvature facing the object side. It is composed of a positive third lens L_3 directed toward
In an objective lens for an endoscope with an aperture diaphragm placed between lens L_2 and third lens L_3, (1) 0.60<|f_1/f|<0.70(2) n_
2>1.60 ν_2<45.0(3)n_3>1.6
0 ν_3>50.0 (4) ν_4<40.0 (5) n_5>1.60 ν_5>50.0 However, f_1: Focal length of the first lens f: Combined focal length of the entire system n_2, n_3, n_5 : Convex lens L of second lens L_2, third lens L_3, and fourth cemented lens L_4+L_5
Refractive index for the d-line of the glass material used in _5 ν_2, ν_3, ν_4, ν_5: second lens L_2,
An objective lens for an endoscope, characterized in that it satisfies the condition of the number of glass materials used in the third lens L_3, the concave lens L_4 of the fourth cemented lens L_4+L_5, and the convex lens L_5 of the fourth cemented lens L_4+L_5.