Zoom optical system for endoscope and endoscope
阅读说明:本技术 内窥镜用变倍光学系统及内窥镜 (Zoom optical system for endoscope and endoscope ) 是由 那须幸子 于 2019-02-19 设计创作,主要内容包括:内窥镜用变倍光学系统从物体侧开始依次具备有负焦度的第一透镜组和有正焦度并能够在光轴上移动的第二透镜组。所述第一透镜组从物体侧开始依次具有凹面朝向像侧的负透镜和凸面朝向物体侧的正透镜,所述第二透镜组具有与凸面朝向物体侧的正透镜接合而成的接合透镜。关于所述第一、第二透镜组各自的合成焦距f<Sub>1</Sub>[mm]、f<Sub>2</Sub>[mm]、远距离观察时的整个系统的合成焦距f<Sub>w</Sub>[mm]、放大观察时的整个系统的合成焦距f<Sub>t</Sub>[mm]、以及所述第一透镜组内在最靠像侧的正透镜的焦距f<Sub>s1</Sub>满足0.6<|f<Sub>s1</Sub>/f<Sub>1</Sub>|<1.6、1.2<f<Sub>t</Sub>/f<Sub>w</Sub><1.4、0.5<|f<Sub>2</Sub>/f<Sub>1</Sub>|<0.8。(The zoom optical system for an endoscope includes, in order from the object side, a first lens group having negative power and a second lens group having positive power and being movable on the optical axis. The first lens group includes, in order from the object side, a negative lens having a concave surface facing the image side and a positive lens having a convex surface facing the object side, and the second lens group includes a positive lens having a convex surface facing the object sideA cemented lens in which positive lenses are cemented. A combined focal length f of the first and second lens groups 1 [mm]、f 2 [mm]Synthetic focal length f of the entire system for long-distance observation w [mm]Synthetic focal length f of the whole system under magnification observation t [mm]And a focal length f of a positive lens closest to an image side in the first lens group s1 Satisfies 0.6 < | f s1 /f 1 |<1.6、1.2<f t /f w <1.4、0.5<|f 2 /f 1 |<0.8。)
1. A variable power optical system for an endoscope, used for an endoscope objective lens unit,
the image pickup device includes, in order from an object side:
a first lens group having negative power; and
a second lens group having a positive power,
the optical image is magnified by moving the second lens group between a wide-angle end position and a telephoto end position in an optical axis direction with respect to the first lens group as a fixed lens group while keeping a distance from a lens surface closest to an object side of the first lens group to an image surface constant,
the first lens group
A negative lens having a concave surface facing the image side and a positive lens having a convex surface facing the object side in this order from the object side,
the second lens group
A positive lens having a convex surface facing the object side and a cemented lens formed by cementing a negative lens and a positive lens in this order from the object side,
setting a composite focal length of the first lens group to f1Setting a composite focal length of the second lens group to f2Setting a composite focal length of the entire system when the second lens group is at the wide-angle end position as fwSetting a composite focal length of the entire system when the second lens group is at the telephoto end position as ftSetting a focal length of the positive lens in the first lens group to fs1And then, satisfy:
(1)0.6<|fs1/f1|<1.6、
(2)1.2<ft/fw<1.4、
(3)0.5<|f2/f1|<0.8,
f1、f2、fw、ftin nm.
2. The variable power optical system for an endoscope according to claim 1,
satisfy (4)2.0 < | fs1/fw|<4.0。
3. The variable power optical system for an endoscope according to claim 1 or 2,
satisfies (5)2.0 < | f1/fw|<4.0。
4. The variable power optical system for an endoscope according to any one of claims 1 to 3,
when the curvature radius of the object side surface of the positive lens in the first lens group is rp1, the curvature radius of the image side surface of the positive lens in the first lens group is rp2, and SF is defined1When (rp1+ rp2)/(rp1-rp2),
satisfies (6) -8.0 < SF1<-2.0,
The units of rp1 and rp2 are mm, and rp2 ≠ rp 1.
5. The variable power optical system for an endoscope according to any one of claims 1 to 4,
and a third lens group which is a fixed lens group including a positive lens having at least a convex surface facing the object side on the image side with respect to the second lens group.
6. The variable power optical system for an endoscope according to any one of claims 1 to 5,
a stop is disposed on the object side of the second lens group between the first lens group and the second lens group,
the stop moves integrally with the second lens group.
7. An endoscope, comprising:
the variable power optical system for an endoscope according to any one of claims 1 to 6; and
and an imaging element that receives light of an image of the object imaged by the variable magnification optical system for an endoscope.
Technical Field
The present invention relates to a variable power optical system for an endoscope used for an endoscope objective lens unit, and an endoscope.
Background
Nowadays, endoscopes are used for examining living tissues inside the human body. An endoscope includes an imaging element for imaging a living tissue illuminated with illumination light at a distal end portion inserted into a human body, and an objective lens unit attached to the imaging element. In order to miniaturize the front end portion of the objective lens unit, the objective lens unit is required to be extremely small in size and to have high optical performance.
In order to observe a lesion in a detailed manner, an endoscope is equipped with a variable magnification optical system having a variable magnification function. Since it is necessary to enlarge a diseased portion while keeping a constant distance from the lens tip on the object side to the image plane, a configuration having at least one movable lens group is generally used as such a variable power optical system.
In such a variable power optical system, when the first lens group closest to the object side is configured by a lens group having positive power, it is easy to correct aberrations in each positive lens group, so that it is possible to suppress performance degradation due to variable power.
In the case where the first lens group closest to the object side is configured by a lens group having negative power, the total length of the optical system can be shortened, but since the lens group having positive power moves and changes in aberration become large, it is necessary to move other lenses in order to suppress the influence thereof.
For example, a high-performance objective optical system corresponding to a high-pixel image pickup element is known as follows: focusing is possible according to a change in the object point distance and a change in the angle of field hardly occurs at that time (patent document 1).
In this objective optical system, the negative first lens group, the positive second lens group, the aperture stop, and the positive third lens group are arranged in this order from the object side, and focusing is performed for a change in the object point distance by moving only the second lens group, and predetermined conditions are satisfied with respect to the maximum half field angle at the time of long-distance observation, the maximum half field angle at the time of short-distance observation, the focal length of the first lens group, and the focal length of the entire system at the time of long-distance observation.
Disclosure of Invention
Problems to be solved by the invention
In the objective optical system described above, although the field angle hardly changes when the magnification is changed, the half field angle at the time of long distance observation is 80.8 degrees at the maximum (see section 0118).
In the current endoscope, a wide angle of visibility is required while maintaining the variable magnification, and for example, the angle of visibility is more than 160 degrees (half field angle 80 degrees) and preferably 165 degrees or more in the long-distance observation.
Accordingly, an object of the present invention is to provide a variable power optical system for an endoscope and an endoscope that have a wide angle of visibility in normal observation (in long-distance observation) in spite of their small size, and that maintain lens performance suitable for observation without reducing magnification in magnification observation.
Means for solving the problems
An aspect of the present invention is a variable power optical system for an endoscope used for an endoscope objective lens unit. The zoom optical system for endoscope
The image pickup device includes, in order from an object side:
a first lens group having negative power; and
a second lens group having a positive power,
the second lens group is moved between a wide-angle end position and a telephoto end position in an optical axis direction with respect to the first lens group as a fixed lens group while keeping a distance from a most object-side lens surface of the first lens group to an image surface constant, thereby magnifying an optical image.
The first lens group
A negative lens having a concave surface facing the image side and a positive lens having a convex surface facing the object side in this order from the object side,
the second lens group
The lens includes, in order from the object side, at least a positive lens having a convex surface facing the object side and a cemented lens formed by cementing a negative lens and a positive lens.
Setting a composite focal length of the first lens group to f1[mm]Setting a composite focal length of the second lens group to f2[mm]Setting a composite focal length of the entire system when the second lens group is at the wide-angle end position as fw[mm]Setting a composite focal length of the entire system when the second lens group is at the telephoto end position as ft[mm]Setting a focal length of the positive lens in the first lens group to fs1And then, satisfy:
(1)0.6<|fs1/f1|<1.6、
(2)1.2<ft/fw<1.4、
(3)0.5<|f2/f1|<0.8。
preferably, the variable power optical system for an endoscope satisfies:
(4)2.0<|fs1/fw|<4.0。
further, it is preferable that the variable magnification optical system for an endoscope satisfies:
(5)2.0<|f1/fw|<4.0。
preferably, a radius of curvature of an object-side surface of the positive lens in the first lens group is rp1[ mm ]]The curvature radius of the image-side surface of the positive lens in the first lens group is rp2(rp2 ≠ rp1) [ mm]Definition of SF1When (rp1+ rp2)/(rp1-rp2),
the variable power optical system for an endoscope satisfies:
(6)-8.0<SF1<-2.0。
preferably, the variable power optical system for an endoscope includes a third lens group which is a fixed lens group on the image side with respect to the second lens group, and the third lens group includes at least a positive lens having a convex surface facing the object side.
Preferably, a stop is disposed on the object side of the second lens group between the first lens group and the second lens group,
the stop moves integrally with the second lens group.
Another aspect of the present invention is an endoscope including:
a variable power optical system for the endoscope; and
and an imaging element that receives light of an image of the object imaged by the variable magnification optical system for an endoscope.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the variable power optical system for an endoscope and the endoscope described above, although small in size, there is a wide angle of visibility at the time of normal observation (at the time of long-distance observation), and lens performance suitable for observation can be maintained without reducing the magnification at the time of magnification observation.
Drawings
Fig. 1 is a view schematically showing an example of the configuration of an endoscope in which the variable magnification optical system for an endoscope according to the present embodiment is mounted.
Fig. 2 (a) and (b) are views showing an example of the configuration of the variable magnification optical system for an endoscope according to the embodiment.
Fig. 3 (a) and (b) are views showing an example of the configuration of the variable magnification optical system for an endoscope according to another embodiment.
Fig. 4 (a) and (b) are views showing an example of the configuration of a variable magnification optical system for an endoscope according to still another embodiment.
Fig. 5 (a) and (b) are views showing an example of the configuration of a variable magnification optical system for an endoscope according to still another embodiment.
Fig. 6 (a) and (b) are views showing an example of the configuration of a variable magnification optical system for an endoscope according to still another embodiment.
Fig. 7 (a) and (b) are views showing an example of the configuration of a variable magnification optical system for an endoscope according to still another embodiment.
Fig. 8 (a) to (d) are various aberration diagrams at the wide-angle end position of the second lens group G2 in example 1, and (e) to (h) are various aberration diagrams at the telephoto end position of the second lens group G2 in example 1.
Fig. 9 (a) to (d) are various aberration diagrams at the wide-angle end position of the second lens group G2 in example 2, and (e) to (h) are various aberration diagrams at the telephoto end position of the second lens group G2 in example 2.
Fig. 10 (a) to (d) are various aberration diagrams at the wide-angle end position of the second lens group G2 in example 3, and (e) to (h) are various aberration diagrams at the telephoto end position of the second lens group G2 in example 3.
Fig. 11 (a) to (d) are various aberration diagrams at the wide-angle end position of the second lens group G2 in example 4, and (e) to (h) are various aberration diagrams at the telephoto end position of the second lens group G2 in example 4.
Fig. 12 (a) to (d) are various aberration diagrams at the wide-angle end position of the second lens group G2 in example 5, and (e) to (h) are various aberration diagrams at the telephoto end position of the second lens group G2 in example 5.
Fig. 13 (a) to (d) are various aberration diagrams at the wide-angle end position of the second lens group G2 in example 6, and (e) to (h) are various aberration diagrams at the telephoto end position of the second lens group G2 in example 6.
Detailed Description
The following describes the variable magnification optical system for an endoscope and the endoscope according to the present embodiment with reference to the drawings. Fig. 1 is an external view showing an external appearance of an
As shown in fig. 1, the
The variable power
Fig. 2 (a) and (b) are views showing an example of the configuration of the endoscopic magnification-varying
As shown in fig. 2 (a) and (b), the endoscopic magnification-varying
With the second lens group G2 at the wide-angle end position, normal observation (telephoto observation) is performed in the
The first lens group G1 includes, in order from the object side, at least a negative lens (lens L1 in the example of fig. 2) having a concave surface facing the image side and a positive lens L3 having a convex surface facing the object side, and is a lens group having negative power disposed on the object side with respect to the stop S. By "at least have" is meant that there may be other optical elements such as a lens, a flat plate, etc. between the lens L1 and the lens L3 in the first lens group G1, and there may be optical elements on the image side of the lens L3. The same meaning is also expressed as "having at least" in the second lens group G2 and the third lens group G3, which will be described later. As shown in fig. 2 (a), the first lens group G1 includes a positive lens L2 whose object-side surface is a flat surface and whose image-side surface is a convex surface.
The second lens group G2 is a lens group having positive power disposed immediately behind the stop S, and is configured to include, in order from the object side, a lens L4 which is a positive lens having a convex surface facing the object side, and a cemented lens CL1 formed by cementing two positive and negative lenses L5 and L6, in order to suppress occurrence of chromatic aberration. In the example shown in fig. 2 (a), the second lens group G2 includes a lens L7 that is a positive lens on the image side of the cemented
In the cemented lens CL1, the lens L5 that is a negative lens is disposed on the object side, and the lens L6 that is a positive lens is disposed on the image side.
In order to magnify an optical image formed on the light receiving surface of the imaging element, the second lens group G2 moves in the optical axis AX direction integrally with the stop S. By moving the second lens group G2 integrally with the stop S, occurrence of astigmatism when the second lens group G2 is at the telephoto end position can be effectively suppressed.
The stop S is a plate-like member having a predetermined circular opening centered on the optical axis AX, or a light shielding film formed by coating a region other than a predetermined circular region centered on the optical axis AX on the object side surface of the lens L4, specifically, on the lens surface of the second lens group G2 closest to the stop S in the example shown in fig. 2 (a). The thickness of the aperture S is extremely thin compared to the thickness of each optical lens constituting the variable magnification
On the image side of the second lens group G2, a third lens group G3 is disposed. The third lens group G3 is composed of a lens L8 which is a positive lens having positive power and a convex surface facing the object side. The third lens group G3 is a fixed lens group, like the first lens group G1. Although the third lens group G3 is provided in the example shown in fig. 2 (a), the third lens group G3 may not be provided. The third lens group G3 is preferably provided in view of suppressing the exit angle of light from the exit pupil at the time of magnification variation toward the imaging element by providing the third lens group G3 as a positive lens having a convex surface directed to the object side.
The lens group may be a lens group composed of a single lens, like the third lens group G3, in addition to a configuration in which a plurality of lenses are provided, like the first lens group G1 or the second lens group G2.
In the variable power
In addition, by disposing the cemented lens CL1 near the center of the second lens group G2, chromatic aberration variation at the time of magnification variation can be suppressed.
Here, when the combined focal length of the first lens group G1 is set to f1[mm]F is the combined focal length of the second lens group G22[mm]Setting the composite focal length of the entire system at the wide-angle end position of the second lens group G2 as fw[mm]The combined focal length of the entire system at the telephoto end position of the second lens group G2 is set to ft[mm]The focal length of the positive lens (lens L3 in the example shown in fig. 2 (a)) located on the most image side in the first lens group G1 is set to fs1The variable power
0.6 < | f of formula (1)s1/f1|<1.6、
Formula (2)1.2 < ft/fw<1.4、
0.5 < | f of formula (3)2/f1|<0.8。
The above expression (1) indicates the focal length f of the lens L3 which is a meniscus lens in the first lens group G1s1Combined focal length f with the first lens group G11The ratio of (a) to (b). Satisfying the expression (1) makes it possible to reduce the diameter of the variable power
The above equation (2) represents the focal length f of the entire system at the time of normal observation (distant observation)wAnd the focal length f of the whole system under magnification observationwRatio f oft/fwThe range of (1). The expression (2) is a conditional expression for bringing the magnification of the image into an appropriate range with respect to the observation distance. If ratio ft/fwWhen the magnification is 1.4 or more, the variation in F number due to the magnification change becomes large, and the resolution in the enlarged view is reduced. If ratio ft/fwWhen the magnification becomes 1.2 or less, the image magnification during the enlarged observation becomes small, and the image cannot be observed sufficiently.
The above formula (3) shows the combined focal length f of the second lens group G22Combined focal length f with the first lens group G11Range of ratios of (a) to (b). By satisfying the formula (3), the zoom
Therefore, by configuring the variable power
Fig. 3 (a) and (b) are views showing an example of the configuration of the variable magnification optical system for
As shown in fig. 3 (a) and (b), the endoscopic magnification-varying
In contrast to the configuration of the variable power
In the case of such a configuration, by satisfying the above-described equations (1) to (3), it is possible to reduce the diameter of the zoom
Fig. 4 (a) and (b) are views showing an example of the configuration of the endoscopic magnification-varying
As shown in fig. 4 (a) and (b), the endoscopic magnification-varying
Although the configuration is the same as that of the variable power optical system for an
Even in the case of such a configuration, by satisfying the above-described equations (1) to (3), it is possible to reduce the diameter of the zoom
Fig. 5 (a) and (b) are views showing an example of the configuration of the endoscopic magnification-varying
As shown in fig. 5 (a) and (b), the endoscopic magnification-varying
In comparison with the configurations of the variable magnification optical system for an
Even in the case of such a configuration, by satisfying the above-described equations (1) to (3), it is possible to reduce the diameter of the zoom
Fig. 6 (a) and (b) are views showing an example of the configuration of the endoscopic magnification-varying
As shown in fig. 6 (a) and (b), the endoscopic magnification-varying
In comparison with the configurations of the variable magnification optical system for an
Even in the case of such a configuration, by satisfying the above-described equations (1) to (3), it is possible to reduce the diameter of the zoom
Fig. 7 (a) and (b) are views showing an example of the configuration of the endoscopic magnification-varying
As shown in fig. 7 (a) and (b), the endoscopic magnification-varying
Although the configuration is the same as that of the variable power
Even in the case of such a configuration, by satisfying the above-described equations (1) to (3), it is possible to reduce the diameter of the zoom
The configuration of the variable magnification
That is, according to an embodiment of the variable magnification optical system for
2.0 < | f of formula (4)s1/fw|<4.0。
Expression (4) indicates the focal length f of the lens L3 which is a positive lens on the side closest to the stop S in the first lens group G1s1Focal length f of the whole system in comparison with the conventional observation (long-distance observation)wRange of ratios of (a) to (b). By satisfying the formula (4), it is possible to suppress aberration occurring in the first lens group G1 and to suppress a change in lens performance at the time of magnification change. Absolute value of ratio | fs1/fwIf | becomes 4.0 or more, the positive power of the lens L3 becomes weak, and it becomes difficult to cancel out the aberration occurring in the negative lens. In addition, if the lens aberration is to be suppressed within an appropriate range, the angle of visibility is narrowed. Absolute value of ratio | fs1/fwIf | becomes 2.0 or less, since the positive power of the lens L3 becomes too strong, the occurrence of distortion aberration becomes serious and peripheral resolution decreases in normal observation. In addition, it becomes difficult to correct aberrations occurring in the positive lens during magnification observation, and therefore it becomes difficult to maintain optical performance.
In addition, according to an embodiment of the variable magnification optical system for
2.0 < | f of formula (5)1/fw|<4.0。
Expression (5) is a composite focal length f of the first lens group G11Focal length f of the whole system in comparison with the conventional observation (long-distance observation)wRatio of (a) | f1/fwThe range of |And (5) enclosing. By satisfying the conditional expression (5), the effective diameter of the first lens group G1 can be suppressed. Absolute value of ratio | f1/fwIf | is 2.0 or less, the negative power of the first lens group G1 becomes stronger, and the negative power of the object side lens L1 becomes stronger, so that coma aberration becomes larger. Absolute value of ratio | f1/fwIf | becomes 4.0 or more, in order to secure negative power of the first lens group G1, it is necessary to increase the effective diameter of the negative lens located on the most object side.
In addition, according to an embodiment of the variable magnification optical system for
formula (6) -8.0 < SF1<-2.0。
Here, the radius of curvature of the object-side surface of the positive lens closest to the image side in the first lens group G1, lens L3 in the example shown in fig. 2 (a), is rp1[ mm []The curvature radius of the image-side surface of the most image-side positive lens in the first lens group G1 is rp2(rp2 ≠ rp1) [ mm []When, define SF1=(rp1+rp2)/(rp1-rp2)。
SF1The shape of the most image-side positive lens in the first lens group G1, lens L3 in the example shown in fig. 2 (a), is defined. By satisfying the formula (6), it is possible to suppress image distortion caused by the lens at the time of normal observation (long-distance observation) while maintaining a state where the visible angle is wide, and it is possible to suppress a change in lens aberration (caused by decentering) caused by the center of the lens being deviated from the
Next, the lens performance of the configuration of the variable power
(example 1)
The configuration of the variable magnification
The lower column (various data) of table 1 shows the specifications (effective F-number, combined focal length [ mm ] of the entire system, optical magnification, half field angle [ degree ], image height [ mm ], group interval D6[ mm ], group interval D14[ mm ]) of example 1.
The group interval D6 is the interval between the first lens group G1 and the second lens group G2. The group interval D14 is the interval between the second lens group G2 and the third lens group G3. The group interval D6 and the group interval D14 vary depending on the magnification-varying position (wide-angle end position and telephoto end position). In table 1, the wide-angle end position at which the variable magnification
[ TABLE 1 ]
Fig. 8 (a) to (d) are various aberration diagrams when the second lens group G2 is at the wide-angle end position in example 1. Fig. 8 (e) to (h) are various aberration diagrams at the telephoto end position of the second lens group G2 in example 1. FIG. 8 (a) and (e) show spherical aberration and axial chromatic aberration on the d-line, g-line (wavelength 436nm) and C-line (wavelength 656 nm). In fig. 8, (b) and (f) show chromatic aberration of magnification for d-line, g-line, and C-line. In fig. 8 (a), (b), (e), and (f), the solid line indicates the aberration in the d-line, the broken line indicates the aberration in the g-line, and the alternate long and short dash line indicates the aberration in the C-line. Fig. 8 (c) and (g) show astigmatism. In fig. 8 (c) and (g), the solid line represents the sagittal component "S" and the broken line represents the radial component "M". Fig. 8 (d) and (h) show distortion aberrations. In fig. 8, (a) to (c) and (e) to (g) have vertical axes representing image heights and horizontal axes representing aberration amounts. In fig. 8, (d) and (h) have vertical axes representing image height and horizontal axes representing distortion factor (%). The descriptions of table 1 of example 1 and (a) to (h) of fig. 8 are also applied to the tables and drawings of the following examples.
In example 1, the half angle of view of the second lens group G2 at the wide-angle end position was set to 85.6 degrees (visible angle was 171.2 degrees), and the effective diameter of the lens L1 was suppressed, so that the entire size of the variable power
(example 2)
The configurations of the variable magnification
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