JP2000330019A - Endoscope objective variable power optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small-sized and high-performance objective variable power optical system of a bifocal type which does not change an object-image distance at the time of variable power in spite of simple constitution consisting of just one group of a lens group which moves at the time of the variable power. SOLUTION: This optical system comprises, successively from an object side, a negative first lens group 10, a brightness stop S, a positive second lens group 20 and a third lens group 30 having negative refracting power. At the time of the variable power, the first lens group 10 and the third lens group 30 are immobile and the second lens group 20 moves at two different points which do not change the object image distance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective zoom optical system used for an endoscope, and more particularly to a bifocal type objective zoom optical system.

[0002]

2. Description of the Related Art In recent years, there is an increasing need for magnifying observation in endoscopes. However, in endoscopes, there is a restriction that the size of the distal end cannot be increased and operability cannot be reduced. It is difficult to adopt a configuration in which zooming (magnification) and focusing (focusing) are performed by separate lenses (groups), like a zoom lens for a camera.
That is, with such a configuration, the number of movable lens groups increases, and the mechanical moving mechanism becomes complicated.
This leads to an increase in the size of the objective optical system. Therefore, conventionally, for example,
JP-A-51-44937 and JP-A-1-2792
By moving one lens group as in the objective variable power optical system described in Japanese Patent Application Publication No. 19-1992, a normal observation state (short focal length) with a viewing angle of about 120 ° and a close-up magnification observation state (long focal length) Distance) can be switched between two focal lengths (2
Focus type).

However, in such a conventional endoscope, the object point moves during zooming (the distance between object images changes).
For this reason, focusing (movement of the tip of the insertion portion in the body) is required at the same time as zooming, and there is a problem in operability, and improvement has been desired. In addition, depending on the part of the living body, it may not be possible to approach at the time of magnifying observation. Therefore, an objective variable magnification optical system having a constant object-image distance has been desired.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a small, high-performance bifocal type objective lens which has a simple structure in which only one lens unit moves during zooming, but does not change the distance between object images during zooming. The objective is to obtain a magnification optical system.

[0005]

SUMMARY OF THE INVENTION An endoscope objective variable power optical system according to the present invention comprises, in order from the object side, a first lens unit having a negative refractive power, a brightness stop, and a second lens unit having a positive refractive power. And a third lens unit having a negative refractive power. During zooming, the first lens unit and the third lens unit do not move, and the second lens unit does not change the object-image distance on the optical axis. Is moved to two different points.

[0006] The endoscope objective variable power optical system of the present invention preferably satisfies the following conditional expression (1). (1) 0.5 <Y / f2 <0.8 (2) 0.05 <| Y / f3 | <0.2, where Y: maximum image height, fi: focal length of the ith lens group (i = 1, 2, 3).

The first lens group comprises a negative single lens,
It is preferable to satisfy the following conditional expression (3). (3) 0.5 <| Y / f1 | <0.8.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An endoscope objective variable power optical system according to the present invention has a negative first lens group 10, a brightness stop S, and a , A positive second lens group 20 and a negative third lens group 30. In the objective variable power optical system, the first lens group 10 and the third lens group 30 do not move during zooming, and the second lens group 20 moves to two points on the optical axis that do not change the object-image distance. I do.

The objective optical system for an endoscope of the present invention has a three-group structure as described above. The first negative lens group is immobile, and only the second positive lens group is moved. Has a doubling effect. If the image plane is fixed and only the second lens group is moved, it is inevitable that the object point moves. It is possible to make the distance between object images constant without moving the object point, for example, by moving the negative third lens group so as to compensate for the movement of the object point by the second lens group. However, an increase in the number of movable lens groups causes an increase in the size of the entire lens system, which is not preferable for an endoscope. Therefore, by fixing the third lens group and moving only the second lens group, a bifocal type objective variable magnification optical system in which the object-image distance does not change due to the magnification change is obtained.

A specific description will be given. At the time of zooming, assuming that the third lens group 30 is movable and moving so that the object-image distance becomes constant, the movement trajectory of the third lens group 30 becomes parabolic as shown in FIG. Become. Therefore, the third
The lens group 30 has two different focal lengths (f1 and f2)
And the position in the optical axis direction becomes the same. When the third lens group 30 is fixed at this position and the second lens group 20 is moved to change the magnification, the distance between the object and the image can be equalized at the two focal lengths f1 and f2. That is, two focal lengths at which the position of the third lens group 30 in the optical axis direction is the same are determined from the movement trajectory for keeping the object-image distance constant when the third lens group 30 is assumed to be movable. By selecting and fixing, by moving only one lens group (the second lens group 20), it is possible to obtain a bifocal objective variable magnification optical system in which the distance between object images does not change at two focal lengths. .

The objective variable power optical system used only at two focal lengths includes, in order from the object side, a negative lens group and a positive lens group.
It can also be obtained in a group configuration. On the other hand, in the three-unit configuration of the present invention, since the negative lens unit (third lens unit) is on the image side of the second lens unit that performs the zooming action,
The refractive power of the lens group can be increased. As a result, the amount of movement of the second lens group for obtaining the required magnification can be reduced, so that the mechanical load can be reduced as compared with the two-group configuration, and the overall size of the optical system can be reduced. .

Conditional expression (1) relates to the refractive power of the second lens group. Beyond the lower limit of conditional expression (1), the second
When the positive refracting power of the lens unit becomes weak, the amount of movement of the second lens unit becomes large in order to obtain a required magnification, which causes an increase in the size of the optical system. Also, the F number at the long focal length extremity increases. If the refracting power of the second lens unit is increased beyond the lower limit of the conditional expression (1), it becomes difficult to correct various aberrations from the short focal length end to the long focal length end in a well-balanced manner. In particular, the field curvature at the long focal length end becomes under.

Condition (2) relates to the refractive power of the third lens group. Beyond the lower limit of condition (2), the third
If the negative refractive power of the lens group becomes too weak, it becomes impossible to increase the positive refractive power of the second lens group, resulting in an increase in the size of the optical system. If the refracting power of the third lens unit is increased beyond the upper limit of the conditional expression (2), the exit pupil position cannot be sufficiently moved away from the image plane at the short focal length extremity, and good telecentricity cannot be obtained. When applied to an electronic endoscope using a color image sensor, problems such as color unevenness occur.

Condition (3) relates to the refractive power of the first lens unit. When the lower limit of conditional expression (3) is exceeded, a wide viewing angle at the short focal length extremity and a back focus required for arranging the filters cannot be obtained. If the upper limit of conditional expression (3) is exceeded, the back focus becomes too long and the overall length (the distance from the object-side surface of the lens closest to the object in the first lens group to the image plane) becomes long. Therefore, the bending operability of the distal end of the scope is reduced.

Next, a specific embodiment will be described. In the various aberration diagrams,
D in the chromatic aberration diagram and the magnification chromatic aberration diagram represented by spherical aberration
Line, g line, and C line are aberrations for each wavelength,
S is sagittal, M is meridional. 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 (the air-equivalent distance from the most image side surface to the image surface), M is lateral magnification, u-1 is object distance, r is radius of curvature, d is lens thickness or lens interval, N
_d indicates the refractive index of the d-line, and ν indicates the Abbe number. Numerical values having a width in the column d are positions before and after switching to the bifocal position which takes one of the displayed numerical values.

[Embodiment 1] FIGS. 1 to 3 show Embodiment 1 of an endoscope objective variable power optical system according to the present invention. FIG. 1 is a lens configuration diagram. The first lens group 10 includes a negative single lens, and the second lens group 20 includes, in order from the object side, a positive lens and a cemented lens of a positive lens and a negative lens. , Third
The lens group 30 includes a single negative lens. r10
-R11 are filters G placed in front of the imaging surface of the imaging device. The aperture stop S moves integrally with the second lens group. 2 and 3 show various aberration diagrams of the endoscope objective variable power optical system at the short focal length position and the long focal length position, respectively, and Table 1 shows numerical data thereof.

[0017]

[Table 1] F _NO = 1: 4.6-7.0 f = 1.01-2.52 (magnification ratio; 2.50) u-1 = 10 W = 60.2-17.6 f _B = 1.12-1.12 (d9 + d10 / Nd10) M =- 0.093- -0.289 Surface No. rd Nd ν 1 ∞ 0.40 1.88300 40.8 2 1.391 2.70-0.60--Brightness aperture ∞ 0.41--3 2.503 1.50 1.88300 40.8 4 -1.954 0.05--5 -9.679 0.70 1.49700 81.6 6 -0.900 0.25 1.84666 23.8 7 -3.339 0.48-2.58--8 -4.372 0.30 1.76182 26.5 9 ∞ 0.20--10 ∞ 1.40 1.51633 64.1 11 ∞---

Embodiment 2 FIGS. 4 to 6 show Embodiment 2 of the endoscope objective variable power optical system of the present invention. FIG. 4 is a lens configuration diagram, FIGS. 5 and 6 are aberration diagrams of the endoscope objective variable power optical system at the short focal length position and the long focal length position, respectively, and Table 2 shows numerical data thereof. The basic lens configuration is the same as in the first embodiment.

[0019]

[Table 2] F _NO = 1: 4.7-6.4 f = 1.04-1.93 (magnification ratio; 1.86) u-1 = 10 W = 57.2-25.1 f _B = 1.12-1.12 (d9 + d10 / Nd10) M =- 0.098- -0.203 Surface No. rd Nd ν 1 ∞ 0.40 1.51633 64.1 2 0.745 1.79-0.75--Brightness aperture ∞ 0.00--3 2.393 0.84 1.88300 40.8 4 -1.881 0.05--5 -191.754 0.70 1.49700 81.6 6 -0.794 0.25 1.84666 23.8 7 -2.043 0.35-1.39--8 -6.914 0.30 1.76182 26.5 9 ∞ 0.20--10 ∞ 1.40 1.51633 64.1 11 ∞---

[Embodiment 3] FIGS. 7 to 9 show Embodiment 3 of the endoscope objective variable power optical system of the present invention. FIG. 7 is a lens configuration diagram. The first lens group 10 is composed of a single negative lens, and the second lens group 20 is composed of a positive lens and a cemented lens of a positive lens and a negative lens in order from the object side. , Third
The lens group 30 includes a cemented lens of a negative lens and a positive lens. r11 to r12 are filters G.
8 and 9 show various aberration diagrams of the endoscope objective variable power optical system at a short focal length position and a long focal length position, respectively.
Is the numerical data.

[0021]

[Table 3] F _NO = 1: 4.6-6.8 f = 1.00-2.33 (magnification ratio; 2.33) u-1 = 10 W = 60.9-20.1 f _B = 1.12-1.12 (d9 + d10 / Nd10) M =- 0.092- -0.253 Surface No. rd Nd ν 1 ∞ 0.40 1.88300 40.8 2 1.338 2.51-0.73--Brightness aperture ∞ 0.19--3 2.616 1.50 1.88300 40.8 4 -1.971 0.10--5 -11.928 0.70 1.58913 61.2 6 -0.870 0.25 1.84666 23.8 7 -3.602 0.32-2.10--8 -6.196 0.25 1.80518 25.4 9 5.888 0.35 1.83481 42.7 10 ∞ 0.20--11 ∞ 1.40 1.51633 64.1 12 ∞---

Table 4 shows values for each conditional expression in each embodiment.

[Table 4] Example 1 Example 2 Example 3 Conditional expression (1) 0.539 0.673 0.557 Conditional expression (2) 0.164 0.104 0.117 Conditional expression (3) 0.597 0.651 0.620 Each example satisfies each conditional expression. Various aberrations are also corrected relatively well. In each embodiment, the object image distance (u-1) before and after the movement of the second lens unit (two focal positions).
Is constant (10 mm). That is, since the first lens group is fixed and the distance from the object-side surface of the first lens group to the image plane is constant, the distance between the object and the image is also constant.

[0023]

According to the present invention, it is possible to obtain a compact and high-performance bifocal type endoscope objective variable power optical system in which the distance between object images does not change at the time of variable power.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of Embodiment 1 of an objective optical system according to the present invention.

FIG. 2 is a diagram illustrating various aberrations at a short focal length position of the lens configuration in FIG. 1;

FIG. 3 is a diagram illustrating various aberrations at a long focal length position of the lens configuration in FIG. 1;

FIG. 4 is a lens configuration diagram of Embodiment 2 of the objective optical system according to the present invention.

FIG. 5 is a diagram illustrating various aberrations at a short focal length position of the lens configuration of FIG. 4;

FIG. 6 is a diagram illustrating various aberrations at a long focal length position of the lens configuration in FIG. 4;

FIG. 7 is a lens configuration diagram of Embodiment 3 of the objective optical system according to the present invention.

8 is a diagram illustrating various aberrations of the lens configuration in FIG. 7 at a short focal length position.

9 is a diagram illustrating various aberrations at a long focal length position of the lens configuration in FIG. 7;

FIG. 10 is a simplified movement diagram of the endoscope objective variable power optical system of the present invention.

FIG. 11 is a diagram illustrating a movement trajectory for maintaining a constant object-image distance when the third lens group is assumed to be movable.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H040 AA02 BA03 CA23 2H087 KA10 PA04 PA18 PA19 PB05 PB06 QA01 QA05 QA18 QA21 QA25 QA33 QA38 QA42 QA45 QA46 RA36 SA14 SA16 SA20 SA63 SA72 SA74 SB02 SB14 SB22 SB23

Claims (3)

[Claims] 1. A first lens unit having a negative refractive power, a brightness stop, and a second lens unit having a positive refractive power, in order from the object side.
The first lens group and the third lens group do not move during zooming, and the second lens group does not change the object-image distance. An endoscope objective variable power optical system, which moves to two different points on an axis. 2. The variable magnification optical system for an endoscope according to claim 1, wherein the following conditional expressions (1) and (2) are satisfied. (1) 0.5 <Y / f2 <0.8 (2) 0.05 <| Y / f3 | <0.2, where Y: maximum image height, fi: focal length of the ith lens group (i = 1, 2, 3). 3. The endoscope objective variable power optical system according to claim 1, wherein said first lens group comprises a single negative lens and satisfies the following conditional expression (3). Double optical system. (3) 0.5 <| Y / f1 | <0.8