JP4142261B2 - Endoscope objective lens system - Google Patents

Description

[0001]
【Technical field】
The present invention relates to an endoscope objective lens system.
[0002]
[Prior art and its problems]
An endoscope objective lens system that requires telecentricity at a wide angle is generally composed of a retrofocus type in which a negative lens group and a positive lens group are arranged in order from the object side. Various aberrations that occur largely in the negative lens group as the angle is widened are corrected in the positive lens group. In particular, in order to correct lateral chromatic aberration, a cemented lens in which a positive lens and a negative lens are bonded is often used. However, it is difficult to join and center a very small lens having a diameter of about several millimeters like an endoscope objective lens system, which requires processing costs.
[0003]
In addition, when an autoclave is used for sterilization of an endoscope, a very high temperature of about 130 ° C. is applied. Therefore, the cemented surface of the cemented lens is peeled off due to high temperature, and the cemented adhesive is denatured and yellowed. Problems arise.
[0004]
As a conventional example that does not use a cemented lens, there is a known three-lens objective lens in which one negative lens is arranged in the first group and two positive lenses are arranged in the second group with the diaphragm interposed therebetween. However, although the number of lenses is small, the lateral chromatic aberration is large and the resolution of the peripheral portion is lowered. An example in which a negative lens and a positive lens are arranged in the first group in front of the aperture stop to reduce lateral chromatic aberration is disclosed in Japanese Patent Laid-Open No. 2-176611, but a positive lens is provided in front of the stop. Since it is disposed, the outer diameter of the first lens is increased, which is disadvantageous as an endoscope objective lens system that is required to be downsized. Further, in order to correct lateral chromatic aberration, it is necessary to reduce the Abbe number of the positive lens, and axial chromatic aberration increases. Further, in order to reduce the telecentric angle, it is necessary to dispose a positive lens in the second group. If the positive lens is disposed in front of the stop, the total length becomes large.
[0005]
OBJECT OF THE INVENTION
The present invention is based on the above awareness of the problems of the conventional endoscope objective lens system, reduces the processing cost without using a cemented lens, and provides resistance even under high temperatures such as an autoclave, with a small number of lenses. An object of the present invention is to provide an endoscope objective lens system that corrects chromatic aberration of magnification and curvature of field without increasing the lens outer diameter.
[0006]
SUMMARY OF THE INVENTION
The present invention focuses on reducing the cost and reducing various aberrations and reducing the outer diameter of the lens by using a ball contact that makes the positive lens and the negative lens contact annularly outside the optical axis instead of using a cemented lens. It was made based on.
That is, according to the present invention, in an endoscope objective lens system having lens groups on the object side and on the image side of the aperture stop, the lens group on the image side with respect to the aperture stop is not contacted on the optical axis. A positive lens and a negative lens each having a convex surface and a concave surface that are annularly contacted off-axis are arranged , and the distance on the optical axis between the positive lens and the negative lens on the image side from the aperture stop is x, and the negative lens of the positive lens is negative. the radius of curvature of the lens side is R (+), the radius of curvature of the positive lens side of the negative lens R (-), the refractive index of the negative lens n (-), the Abbe number [nu (-) and the total When the focal length of the system is f, the following conditional expressions (1) to (5) are satisfied .
(1) 1.71 ≦ | R (+) | / f <4
(2) 1.50 ≦ | R (−) | / f <3
(3) 0.02 <x / f <0.2
(4) 1.75 <n (-)
(5) ν (−) <30
By using a positive lens and a negative lens as a ball contact, it is possible to reduce parts such as a spacing ring and a spacer. The combined power of the positive lens and the negative lens is preferably positive. The order of the positive lens and the negative lens does not matter.
[0007]
The lens group on the object side with respect to the aperture stop can be composed of one negative lens. In addition, the lens group on the image side from the aperture stop can be composed of a positive lens group, a positive lens and a negative lens in contact with the lens in order from the brightness stop side.
[0009]
Furthermore, it is preferable that the following conditional expression (6) is satisfied.
(6) 0.8 <{(2 | R (+) | S (+) − S (+) ² )} ^1/2 /f<1.6
However,
S (+) = d (2 | R (-) | -x ) / 2 (| R (+)-R (-) | + x )
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The objective lens for an endoscope according to the present invention is arranged on the object side with an aperture stop S interposed therebetween, as shown in the lens configuration diagrams of the respective embodiments of FIGS. 1, 3, 5, 7, and 9. It has a negative lens group (front group) 10 and a positive lens group (rear group) 20 on the image side. The positive lens group 20 includes, in order from the stop S side, a first sub group 21 having a positive power and a second sub group 22 having a positive power as a whole. In any of the embodiments, the negative lens group 10 includes a negative single lens, and the first sub group 21 of the positive lens group 20 includes a positive single lens. More specifically, the negative lens group 10 is composed of a single lens whose surface on the object side is flat in Examples 1 to 4, and a single lens whose surface on the object side is concave in Example 5.
[0011]
The second sub group 22 of the positive lens group 20 includes a positive lens 23 and a negative lens 24 in order from the object side except for the third embodiment. In the third embodiment, the negative lens 24 and the positive lens 23 are sequentially formed from the object side. It is made up of. The surface of the positive lens 23 on the negative lens 24 side is a convex surface, and the surface of the negative lens 24 on the positive lens 23 side is a concave surface, and this opposing surface maintains a gap x on the optical axis in a non-contact manner. The ring contacts the optical axis outside the optical axis. All the lenses (groups) are spherical lenses having a rotationally symmetric shape around the optical axis.
[0012]
Conditional expressions (1) and (2) are conditions relating to the radius of curvature of the convex and concave surfaces of the positive lens and negative lens facing each other. When the upper limit of conditional expression (1) is exceeded, correction of lateral chromatic aberration is insufficient. Below the lower limit, coma and spherical aberration are increased.
[0013]
If the upper limit of conditional expression (2) is exceeded, correction of lateral chromatic aberration will be insufficient. Below the lower limit, coma and spherical aberration are increased.
[0014]
Conditional expression (3) is a condition relating to the distance between the positive lens and the negative lens used for ball contact. If the upper limit of the conditional expression (3) is exceeded, the distance between the positive and negative lenses becomes too large, and if an attempt is made to hit the ball without using a spacer, the lens outer diameter becomes large.
[0015]
Conditional expressions (4) and (5) are conditions for the negative lens to be hit. Deviating from this conditional expression results in insufficient correction of the lateral chromatic aberration.
[0016]
Conditional expression (6) is a condition that defines the distance (radius) from the optical axis of an annular line (circle) where the positive lens and the negative lens are in contact. If the upper limit of conditional expression (6) is exceeded, the lens outer diameter will increase. Below the lower limit, the effective diameter at the ball contact surface decreases, and the telecentric angle increases. The increased telecentric angle can be further reduced by disposing a lens on the image side, but this increases the number of lenses.
[0017]
Next, specific numerical examples will be described. In the various aberration diagrams, SA is a spherical aberration, SC is a sine condition, d-line, g-line, and C-line are aberrations for each wavelength, S is sagittal, M is meridional, and Y is image height. In the table, F _NO is the F number, f is the focal length of the entire system, W is the half angle of view (°), F _B is the back focus, m is the lateral magnification, r is the radius of curvature, and d is the lens thickness or lens. The distance, N _d is the refractive index of the d-line, and ν is the Abbe number.
[0018]
[Example 1]
FIG. 1 shows the lens configuration of Example 1, and FIG. 2 shows various aberrations in the lens configuration of FIG. Table 1 shows the numerical data.
[0019]
[Table 1]
F _NO = 1: 1.9
f = 1.00
W = 48.7
F _B = 0.59
m = -0.073
Surface No. r d N _d ν
1 ∞ 0.60 1.45854 68.0
2 0.956 0.18--
Aperture ∞ 0.05--
3 ∞ 1.19 1.72916 54.7
4 -1.046 0.08--
5 2.199 1.02 1.77250 49.6
6 -2.199 0.04--
7 -1.840 0.50 1.92286 18.9
8 -6.150---
[0020]
[Example 2]
FIG. 3 shows the lens configuration of Example 2, and FIG. 4 shows various aberrations in the lens configuration of FIG. Table 2 shows the numerical data.
[0021]
[Table 2]
F _NO = 1: 2.0
f = 1.00
W = 49.7
F _B = 0.50
m = -0.073
Surface No. r d N _d ν
1 ∞ 0.62 1.51633 64.1
2 0.920 0.20--
Aperture ∞ 0.05--
3 ∞ 1.33 1.77250 49.6
4 -1.151 0.08--
5 2.129 1.28 1.77250 49.6
6 -2.627 0.07--
7 -2.279 0.50 1.92286 18.9
8 -36.384---
[0022]
[Example 3]
FIG. 5 shows the lens configuration of Example 3, and FIG. 6 shows various aberrations in the lens configuration of FIG. Table 3 shows the numerical data.
[0023]
[Table 3]
F _NO = 1: 2.3
f = 1.00
W = 49.6
F _B = 0.64
m = -0.070
Surface No. r d N _d ν
1 ∞ 0.69 1.45854 68.0
2 0.958 0.15--
Aperture ∞ 0.05--
3 ∞ 0.98 1.88 300 40.8
4 -1.008 0.09--
5 3.708 0.52 1.92286 18.9
6 1.500 0.05--
7 1.710 0.87 1.77250 49.6
8 -2.827---
[0024]
[Example 4]
FIG. 7 shows the lens configuration of Example 4, and FIG. 8 shows various aberrations in the lens configuration of FIG. Table 4 shows the numerical data.
[0025]
[Table 4]
FNO = 1: 2.3
f = 1.00
W = 59.2
FB = 0.58
m = -0.079
Surface No. r d Nd ν
1 ∞ 0.59 1.88 300 40.8
2 1.255 0.18--
Aperture ∞ 0.05--
3 ∞ 1.28 1.77250 49.6
4 -1.114 0.13--
5 2.177 1.22 1.77250 49.6
6 -2.177 0.10--
7 -1.690 0.57 1.92286 18.9
8 -5.764---
[0026]
[Example 5]
FIG. 9 shows the lens configuration of Example 5, and FIG. 10 shows various aberrations in the lens configuration of FIG. Table 5 shows the numerical data.
[0027]
[Table 5]
F _NO = 1: 2.2
f = 1.00
W = 50.0
F _B = 0.50
m = -0.072
Surface No. r d N _d ν
1 ∞ 0.59 1.51633 64.1
2 0.936 0.20--
Aperture ∞ 0.10--
3 -5.985 1.11 1.72916 54.7
4 -1.017 0.07--
5 2.125 1.34 1.72916 54.7
6 -2.566 0.10--
7 -1.789 0.50 1.84666 23.8
8 -4.005---
[0028]
Table 6 shows values of the conditional expressions for the respective embodiments.
[Table 6]
Example 1 Example 2 Example 3 Example 4 Example 5
Conditional expression (1) 2.199 2.627 1.710 2.177 2.566
Conditional expression (2) 1.840 2.279 1.500 1.690 1.789
Conditional expression (3) 0.040 0.070 0.050 0.100 0.101
Conditional expression (4) 1.92286 1.92286 1.92286 1.92286 1.84666
Conditional expression (5) 18.9 18.9 18.9 18.9 23.8
Conditional expression (6) 0.877 1.354 0.943 1.067 0.989
Each example satisfies each conditional expression, and various aberrations are corrected relatively well.
[0029]
【The invention's effect】
According to the present invention, without using a cemented lens, processing costs are reduced, resistance is maintained even at high temperatures such as an autoclave, and chromatic aberration of magnification and curvature of field can be reduced with a small number of lenses without increasing the outer diameter of the lens. An endoscope objective lens system in which various aberrations are corrected is obtained.
[Brief description of the drawings]
FIG. 1 is a lens configuration diagram of Example 1 of an endoscope objective lens system according to the present invention.
2 is a diagram illustrating various aberrations of the lens configuration in FIG. 1. FIG.
FIG. 3 is a lens configuration diagram of Example 2 of an endoscope objective lens system according to the present invention.
4 is a diagram illustrating various aberrations of the lens configuration in FIG. 3; FIG.
FIG. 5 is a lens configuration diagram of Example 3 of an endoscope objective lens system according to the present invention.
6 is a diagram illustrating various aberrations of the lens configuration in FIG. 5. FIG.
FIG. 7 is a lens configuration diagram of Example 4 of an endoscope objective lens system according to the present invention.
8 is a diagram illustrating various aberrations of the lens configuration in FIG. 7;
FIG. 9 is a diagram illustrating a fifth embodiment of the endoscope objective lens system according to the present invention.
10 is a diagram illustrating various aberrations of the lens configuration in FIG. 9. FIG.

Claims (5)

In an endoscope objective lens system having lens groups on the object side and the image side of the aperture stop,
In the lens group on the image side from the above aperture stop, a positive lens and a negative lens having a convex surface and a concave surface that are non-contact on the optical axis and annularly contact outside the optical axis, respectively, are arranged .
The distance on the optical axis between the positive lens and the negative lens on the image side from the aperture stop is x, the radius of curvature of the negative lens side surface of the positive lens is R (+), and the curvature of the negative lens on the positive lens side is When the radius is R (−) , the refractive index of the negative lens is n (−) , the Abbe number is ν (−), and the focal length of the entire system is f, the following conditional expressions (1) to (5) An endoscope objective lens system characterized by satisfying .
(1) 1.71 ≦ | R (+) | / f <4
(2) 1.50 ≦ | R (−) | / f <3
(3) 0.02 <x / f <0.2
(4) 1.75 <n (-)
(5) ν (−) <30 The endoscope objective lens system according to claim 1, wherein a combined power of the positive lens and the negative lens is positive. The endoscope objective lens system according to claim 1 or 2, wherein the lens group closer to the object side than the aperture stop is composed of one negative lens. 3. The endoscope objective lens system according to claim 1, wherein the lens group on the image side of the brightness stop includes, in order from the brightness stop side, a positive lens group, and the positive lens and the negative lens. Endoscope objective lens system. The endoscope objective lens system according to any one of claims 1 to 4 , further satisfying the following conditional expression (6).
(6) 0.8 <{(2 | R (+) | S (+) − S (+) ² )} ^1/2 /f<1.6
However,
S (+) = d (2 | R (−) | −x ) / 2 (| R (+) − R (−) | + x ).

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