JP4634578B2 - Endoscope objective variable magnification optical system - Google Patents

Description

[0001]
【Technical field】
The present invention relates to an objective variable magnification optical system used for an endoscope.
[0002]
[Prior art and its problems]
In recent years, the need for magnification observation has been increasing in endoscopes, and endoscopes having an objective variable magnification optical system to meet the needs have appeared. Examples of conventional objective variable magnification optical systems for such endoscopes include those described in JP-A-1-279219, JP-A-4-21812, and JP-A-3-145614. These objective variable magnification optical systems of these endoscopes are not sufficiently widened because the incident angle 2ω at the low magnification end is about 100 °. Further, the objective variable magnification optical system described in JP-A-6-317744 has a large number of lenses and a complicated structure.
[0003]
OBJECT OF THE INVENTION
An object of the present invention is to obtain an objective variable magnification optical system used in an endoscope having a simple configuration and an incident angle 2ω at a low magnification end of 130 ° or more.
[0004]
Summary of the Invention
The present invention is an objective variable magnification optical system used for an endoscope, and is composed of a first lens group having a negative power and a second lens group having a positive power in order from the object side. The first lens group is stationary, the second lens group is movable, the first lens group includes at least two negative lenses, and the second lens group is composed of a positive second group a and a second group b. In zooming from the low magnification end to the high magnification end, the second group a moves to the object side, and the second group b moves to correct the movement of the image plane position accompanying the movement of the second group a. The zoom lens is zoomed while maintaining the distance between the object images constant, and satisfies the following conditional expressions (1) and (3) .
(1) (ν1 / f1a + ν2 / f1b) · f1> 50
(3) 0.1 <| f2a / f2b | ≦ 0.33
However,
ν1: Abbe number of the negative lens closest to the object side in the first lens group,
ν2: Abbe number of the negative lens closest to the image side in the first lens group,
f1a: focal length of the negative lens closest to the object side in the first lens group,
f1b: the focal length of the negative lens closest to the image side in the first lens group,
f1: the focal length of the first lens group,
f2a: focal length of group 2a,
f2b: focal length of group 2b,
It is.
[0005]
According to another aspect of the present invention, there is provided an objective variable magnification optical system used for an endoscope, which includes, in order from the object side, a first lens group having a negative power and a second lens group having a positive power. In zooming, the first lens group is stationary, the second lens group is movable, the first lens group includes at least two negative lenses, and the second lens group is sequentially positive from the object side. 2a group and negative 2b group, and when zooming from the low magnification end to the high magnification end, the 2a group moves to the object side, and the 2b group moves to the image plane accompanying the movement of the 2a group. It is characterized by moving so as to correct the movement of the position, and scaling while maintaining a constant distance between the object images, and satisfying the following conditional expressions (1) and (3).
(1) (ν1 / f1a + ν2 / f1b) · f1> 50
(3) 0.1 <| f2a / f2b | ≦ 0.33
However,
ν1: Abbe number of the negative lens closest to the object side in the first lens group,
ν2: Abbe number of the negative lens closest to the image side in the first lens group,
f1a: focal length of the negative lens closest to the object side in the first lens group,
f1b: the focal length of the negative lens closest to the image side in the first lens group,
f1: the focal length of the first lens group,
f2a: focal length of group 2a,
f2b: the focal length of the second group b.
[0006]
It is preferable that the object side negative lens of the first lens group is located closest to the object side, and the object side surface of the negative lens is a flat surface, and satisfies the following conditional expression (2).
(2) 0.05 <| f1a / f1b | <1.2
[0008]
DETAILED DESCRIPTION OF THE INVENTION
As shown in the simplified movement diagrams of FIGS. 9 and 10 , the endoscope objective variable magnification optical system according to the present invention includes, in order from the object side, a first lens group 10 having a negative power and a second lens having a positive power. The distance between the object images does not change (the distance between the object images is kept constant). The first lens group 10 having a negative power does not move during zooming in any of the modes shown in FIGS. On the other hand, the second lens group having a positive power consists of a positive second group a 20a and a second group 20b in the embodiment of FIG. 9, and in the embodiment of FIG. 10, the positive second group a and the negative second lens group. It consists of 2b group. In both the mode of FIG. 9 and the mode of FIG. 10, the second a group 20a and the second b group 20b both move to the object side upon zooming from the low magnification end to the high magnification end. In the aspect of FIG. 10, the distance from the first lens group 10 is once reduced and then expanded, and in the aspect of FIG. 10, the distance from the first lens group 10 is once increased and then reduced. In any aspect, the aperture stop S is disposed between the first lens group 10 and the second lens group 20 and moves together with the second lens group 20.
[0011]
The endoscope objective variable magnification optical system according to the present invention constitutes a so-called retrofocus type by setting the first lens group 10 to a negative power and the second lens group 20 to a positive power. The incident height of the peripheral luminous flux to one lens group 10 is kept small, the increase in the lens diameter is suppressed, and the back focus is sufficiently secured. Here, when trying to obtain a high zoom ratio with a wide incident angle, a large difference occurs in the incident height of the peripheral luminous flux passing through the negative first lens group at the low magnification end and the high magnification end. On the other hand, if the negative first lens group 10 is configured by a single lens, various refractive indexes, particularly coma and astigmatism, are kept high even at a wide incident angle. I have to use glass. However, no such high refractive index glass has a small dispersion, and the chromatic aberration of magnification at the low magnification end is particularly large. Therefore, the negative first lens group 10 is divided into two pieces and a low refractive index glass having a small dispersion is used to reduce lateral chromatic aberration and to keep coma and astigmatism good. ing. Further, by using low refractive index glass for the first lens group 10 having a negative power, the Petzval sum can be improved and the image plane can be flattened.
[0012]
Conditional expression (1) is a condition regarding the Abbe number of two negative lenses included in the first lens group.
If glass having a large dispersion exceeding the lower limit of conditional expression (1) is used, lateral chromatic aberration at low magnification becomes insufficiently corrected.
[0013]
In an endoscope, cleaning after use is extremely important. Considering the ease of cleaning, it is preferable that the most object side lens surface of the first lens group exposed to the outside is a flat surface.
Conditional expression (2) is a condition for maintaining good coma and astigmatism when the most object side lens surface of the first lens unit is a flat surface.
When the lower limit of conditional expression (2) is exceeded, the power of the image side surface of the object side lens in the first lens group becomes too strong, increasing coma and astigmatism. If the power of the lens on the image side of the first lens group increases beyond the upper limit of conditional expression (2), the coma aberration decreases, but the incident height of the lens on the object side increases, and the lens diameter increases. Invite.
[0014]
In the present embodiment, as described above , the second lens group is divided into the second a group and the second b group and moved independently in order to keep the object-image distance constant during zooming. Conditional expression (3) is a condition for appropriately maintaining the powers of the second group a and the second group b when the distance between the object images is kept constant. If the power of the second group a increases beyond the lower limit of conditional expression (3), the amount of movement of the second group b increases, leading to an increase in size. If the power of the second group b increases beyond the upper limit of conditional expression (3), the amount of movement of the second group a increases, leading to an increase in size.
[0015]
Next, specific examples will be described. In the various aberration diagrams, the d-line, g-line, C-line, F-line, and e-line in the chromatic aberration diagram and magnification chromatic aberration diagram represented by spherical aberration are aberrations for each wavelength, S is sagittal, M is meridional, Y is the image height. Further, F _NO is the effective F-number in the table, f is the focal length of the entire system, M is the transverse magnification, 2 [omega is full angle of view (DEG), r is the radius of curvature, d is the lens thickness or distance between lens, Nd is d The refractive index of the line, ν, indicates the Abbe number.
[0018]
[Example 1 ]
1 to 4 show a first embodiment of an endoscope objective variable magnification optical system according to the present invention. The first embodiment is of the type shown in FIG. 9 , that is, the type in which the positive second a group 20a and the second b group 20b are independently moved so as to keep the imaging position constant during zooming (between object images). This is an example of a constant distance type). 1 and 3 are lens configuration diagrams at the minimum magnification and the maximum magnification, respectively. The first lens group 10 includes two negative lenses, and the second lens group 20 includes a positive lens in order from the object side. The positive power second a group 20a composed of a cemented lens of a negative lens and a positive lens and the second b group 20b composed of a positive single lens. The negative lens on the object side of the first lens group 10 is located closest to the object side, and the object side surface of the negative lens is a flat surface. The parallel plane plate on the image side of the second lens group 20 is a filter group G placed in front of the imaging surface of the imaging device. 2 and 4 are diagrams showing various aberrations of the lens configuration shown in FIGS. 1 and 3, respectively, and Table 1 shows numerical data thereof. The aperture stop S is at a position of 0.1 mm on the object side of surface No. 5.
[0019]
[Table 1]
Minimum magnification Maximum magnification
FNO = 1: 4.6 − 7.0
f = 1.40 − 3.45
M = -0.12--0.35 (magnification ratio; 2.9)
Incident angle 2ω = 137.6-42.6 (°)
Object distance = 10 (mm)
Surface No. r d Nd ν
1 ∞ 0.300 1.51633 64.1
2 1.884 1.122--
3 547.264 0.300 1.51633 64.1
4 7.078 3.550-0.366--
5 2.844 0.547 1.88300 40.8
6 -24.257 0.572--
7 5.154 0.474 1.84666 23.8
8 1.390 1.524 1.49700 81.6
9 -5.677 0.200-0.223--
10 7.061 0.525 1.77250 49.6
11 ∞ 1.004-4.165--
12 ∞ 1.300 1.51633 64.1
13 ∞---
[0020]
[Example 2 ]
5 through 8 show a second embodiment of the endoscope objective variable power optical system of the present invention. The second embodiment is the type of Fig. 10, i.e., during zooming, a positive of the 2a group 20a and the negative of the 2b group 20b are moved independently to keep the imaging position to a constant type (object-image This is an example of a constant distance type. 5 and 7 are lens configuration diagrams at the lowest magnification and the highest magnification, respectively. The basic lens configuration is the same as that of the first embodiment except that the second b group 20b is composed of a negative single lens. FIGS. 6 and 8 are graphs showing various aberrations of the lens configuration shown in FIGS. 5 and 7 , and Table 2 shows numerical data thereof. The aperture stop S is at a position of 0.105 mm on the object side of the surface No.5.
[0021]
[Table 2]
Minimum magnification Maximum magnification
FNO = 1: 4.7 − 7.0
f = 1.41 − 3.15
M = -0.13--0.35 (magnification ratio; 2.9)
Incident angle 2ω = 138.5-42.5 (°)
Object distance = 10 (mm)
Surface No. r d Nd ν
1 ∞ 0.300 1.58913 61.2
2 1.587 1.070--
3 -17.754 0.300 1.51633 64.1
4 18.360 3.280-0.429--
5 3.383 0.711 1.88300 40.8
6 -5.693 0.464--
7 5.399 0.400 1.84666 23.8
8 1.270 2.124 1.51633 64.1
9 -2.890 0.586-3.199--
10 -6.300 0.378 1.78472 25.7
11 ∞ 0.418-0.656--
12 ∞ 1.300 1.51633 64.1
13 ∞---
[0022]
Table 3 shows values for each conditional expression in each example.
[ Table 3 ]
Example 1 Example 2
Conditional expression (1) 59.6 58.2
Conditional expression (2) 0.26 0.15
Conditional expression (3) 0.28 0.33
In Examples 1 and 2, each conditional expression is satisfied, and various aberrations are corrected relatively well.
[0023]
【The invention's effect】
According to the present invention, an endoscope objective variable magnification optical system having a simple configuration and a wide incident angle at a low magnification end can be obtained.
[Brief description of the drawings]
FIG. 1 is a lens configuration diagram at a minimum magnification in Example 1 of an endoscope objective variable magnification optical 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 at the maximum magnification of Example 1 of the endoscope objective variable magnification optical 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 at the minimum magnification of Example 2 of the endoscope objective variable magnification optical 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 at the maximum magnification of Example 2 of the endoscope objective variable magnification optical system according to the present invention.
8 is a diagram illustrating various aberrations of the lens configuration in FIG. 7;
FIG. 9 is a simple movement diagram of the endoscope objective variable magnification optical system according to the first embodiment of the present invention.
FIG. 10 is a simple movement diagram of the endoscope objective variable magnification optical system according to the second embodiment of the present invention.

Claims (3)

An objective variable magnification optical system used for an endoscope, comprising, in order from the object side, a first lens group having a negative power and a second lens group having a positive power,
During zooming, the first lens group is stationary and the second lens group is movable,
The first lens group includes at least two negative lenses,
The second lens group is composed of both a positive 2a group and a 2b group, and when zooming from the low magnification end to the high magnification end, the 2a group moves to the object side, and the 2b group is the 2a group. Move so as to correct the movement of the image plane position accompanying the movement of, and scale while keeping the distance between the object images constant,
An endoscope objective variable magnification optical system characterized by satisfying the following conditional expressions (1) and (3):
(1) (ν1 / f1a + ν2 / f1b) · f1> 50
(3) 0.1 <| f2a / f2b | ≦ 0.33
However,
ν1: Abbe number of the negative lens closest to the object side in the first lens group,
ν2: Abbe number of the negative lens closest to the image side in the first lens group,
f1a: focal length of the negative lens closest to the object side in the first lens group,
f1b: the focal length of the negative lens closest to the image side in the first lens group,
f1: the focal length of the first lens group,
f2a: focal length of group 2a,
f2b: the focal length of the second group b. An objective variable magnification optical system used for an endoscope, comprising, in order from the object side, a first lens group having a negative power and a second lens group having a positive power,
  During zooming, the first lens group is stationary and the second lens group is movable,
  The first lens group includes at least two negative lenses,
  The second lens group includes, in order from the object side, a positive second group a and a negative second group b. Upon zooming from the low magnification end to the high magnification end, the second lens group moves to the object side, The 2b group moves so as to correct the movement of the image plane position accompanying the movement of the 2a group, and scales while keeping the distance between the object images constant,
  An endoscope objective variable magnification optical system characterized by satisfying the following conditional expressions (1) and (3):
(1) (ν1 / f1a + ν2 / f1b) · f1> 50
(3) 0.1 <| f2a / f2b | ≦ 0.33
However,
ν1: Abbe number of the negative lens closest to the object side in the first lens group,
ν2: Abbe number of the negative lens closest to the image side in the first lens group,
f1a: focal length of the negative lens closest to the object side in the first lens group,
f1b: the focal length of the negative lens closest to the image side in the first lens group,
f1: the focal length of the first lens group,
f2a: focal length of group 2a,
f2b: the focal length of the second group b. 3. The endoscope objective variable magnification optical system according to claim 1, wherein the object side negative lens of the first lens group is located closest to the object side, and the object side surface of the negative lens is a flat surface. An endoscope objective variable magnification optical system that satisfies conditional expression (2).
(2) 0.05 <| f1a / f1b | <1.2

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