JP2022138071A - Image capturing optical system - Google Patents

Abstract

To provide an image capturing optical system with improved optical performance.SOLUTION: An image capturing optical system 100a comprises a deflection mirror 71, first lens group G1, and second lens group G2 arranged in order from a front side corresponding to the object side. The deflection mirror 71 is located at a position corresponding to an entrance pupil P1 of the first lens group G1. The first lens group G1 has a primary imaging plane IP1 conjugate with a detection plane IP2 between itself and the second lens group G2. The second lens group G2 includes an iris diaphragm 70d, and the deflection mirror 71 and the iris diaphragm 70d are located at conjugate positions.SELECTED DRAWING: Figure 1

Description

The present invention relates to an imaging optical system having an entrance pupil on the object side of the first lens group, and more particularly to an imaging optical system suitable for moving the field of view using a deflecting mirror.

As an optical system including a deflection mirror, for example, there is a confocal microscope equipped with a collimating optical system including an objective lens, a detection optical system having a sensor, and a scan mirror arranged between the collimating optical system and the detection optical system. (See, for example, Patent Document 1, etc.). This type of microscope completes the image by the movement of the scanning mirror.

A moving object imaging device that tracks a moving object using a deflecting mirror placed in front of a camera is known (Patent Document 2). The optical system of Patent Literature 2 is a combination of a camera lens and a deflecting mirror, and is not recognized as having an appropriate optical design.

Special table 2019-511013 WO2018/179829

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described background art, and provides an imaging optical system that enables a field of view to be moved using a deflecting mirror, and that has improved optical performance. With the goal.

In order to solve the above-described problems, an imaging optical system according to the present invention includes, in order from the front side corresponding to the object side, a deflection mirror, a first lens group, and a second lens group. The first lens group is arranged at the position of the entrance pupil of the lens group, the first lens group has a primary imaging plane conjugate with the detection surface between the second lens group, the iris diaphragm is arranged in the second lens group, The deflecting mirror and the iris diaphragm are arranged at conjugate positions.

In the imaging optical system described above, the deflection mirror is arranged at the position of the entrance pupil of the first lens group, and the size and weight of the deflection mirror can be reduced. Furthermore, since the deflecting mirror and the iris diaphragm in the second lens group are arranged at conjugate positions, it is possible to prevent the occurrence of lack of field of view. The position of the entrance pupil of the first lens group coincides with the position of the entrance pupil of the entire system, that is, the imaging optical system, and the deflection mirror is arranged at the position of the entrance pupil of the entire system, that is, the imaging optical system.

In a specific aspect of the invention, the first lens group is telecentric to the rear, and a deflection mirror is positioned at the front focal point of the first lens group. In this case, it is possible to suppress the occurrence of vignetting on the primary imaging plane.

In another aspect of the present invention, the second lens group is telecentric on the front side, and the iris diaphragm is arranged at a back focal position in the front side of the iris diaphragm of the second lens group. In this case, it is possible to provide an optical system with relatively high reliability in which axial misalignment of the second lens group with respect to the first lens group is relatively tolerated.

In yet another aspect of the invention, a liquid lens is provided on the image side of the iris diaphragm. In this case, the operation of the liquid lens is less likely to affect the function of the iris diaphragm.

In yet another aspect of the invention, the liquid lens has refractive power that varies from negative to positive.

In still another aspect of the present invention, the first lens group is a combination of a lens having positive refractive power and a lens having negative refractive power, and the second lens group includes The lens is a combination of lenses with positive refractive power.

In order to solve the above-described problem, the imaging optical system according to the present invention includes a first lens group and a second lens group in order from the front side, which is the object side, and the first lens group is positioned closer to the first lens group than the first lens group. also has an entrance pupil on the object side, a primary imaging plane conjugate with the detection surface between the second lens group, an iris diaphragm arranged in the second lens group, and an entrance pupil of the first lens group and the iris diaphragm are arranged at conjugate positions.

In the imaging optical system, the first lens group has an entrance pupil closer to the object side than the first lens group, and if the deflection mirror is arranged at the position of the entrance pupil, the deflection mirror can be made smaller and lighter. . Furthermore, since the deflecting mirror can be arranged in the second lens group at a position conjugate with the iris diaphragm, it is possible to prevent the occurrence of lack of the field of view.

In still another aspect of the present invention, the imaging optical system further includes a deflection mirror arranged at the position of the entrance pupil of the first lens group.

It is a figure explaining the imaging device containing the imaging optical system of embodiment. FIG. 4 is a side cross-sectional view enlarging the vicinity of the boundary between the first lens group and the second lens group;

An imaging apparatus including an imaging optical system according to an embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a diagram illustrating the configuration of an imaging device 100. The imaging device 100 includes an imaging optical system 100a and an accessory device 100b.

The imaging optical system 100 a is an imaging optical system for visible light, and includes a deflection mirror 71 , a prism mirror 72 , and an image sensor 73 in addition to the main body optical system 70 . The imaging optical system 100a can move the field of view by means of the deflecting mirror 71, and is suitable for observation with a wide field of view through a small window, such as bottle bottom inspection.

The body optical system 70 includes, in order from the front side corresponding to the object side, a first lens group G1 and a second lens group G2, as shown in a cross section along the optical axis OA. The first lens group G1 is an imaging system that forms a primary image of an object to be photographed on a primary imaging plane IP1. an imaging system formed on the top;

The first lens group G<b>1 includes a first lens 10 and a second lens 20 . The first lens 10 has positive refractive power as a whole and includes three lens elements 11 , 12 , 13 . The first lens element 11 and the second lens element 12 have positive refractive power, and the third lens element 13 has negative refractive power.

The second lens 20 of the first lens group G1 has negative refractive power as a whole and includes two lens elements 21 and 22 . The fourth lens element 21 has positive refractive power, the fifth lens element 22 has negative refractive power, and both are cemented.

As described above, the first lens group G1 is a combination of the first lens 10 having positive refractive power and the second lens 20 having negative refractive power, and has positive refractive power as a whole. . The first lens group G1 has a telephoto type arrangement as a result of combining a positive first lens 10 and a negative second lens 20, and an entrance pupil P1 is placed on the object side of the first lens 10. easier to place. Further, the first lens group G1 is telecentric on the rear side, and the front focal position of the first lens group G1 is the position of the entrance pupil P1. Since the first lens group G1 is telecentric on the rear side, it is possible to suppress the occurrence of limb darkening on the primary image plane IP1.

The second lens group G2 includes a third lens 30, a fourth lens 40, an iris diaphragm 70d, a fifth lens 50, and a filter 70f. The third lens 30 has positive refractive power as a whole and includes three lens elements 31 , 32 , 33 . The sixth lens element 31 has negative refractive power, and the seventh lens element 32 and the eighth lens element 33 have positive refractive power. Among these, the sixth lens element 31 and the seventh lens element 32 form a cemented lens having negative refractive power as a whole. In the second lens group G2, the fourth lens 40 has positive refractive power as a whole and includes five lens elements 41,42,43,44,45. The ninth lens element 41 has positive refractive power, the tenth lens element 42 has negative refractive power, and the eleventh lens element 43 and the twelfth lens element 44 have positive refractive power. and the thirteenth lens element 45 has a negative refractive power. Among these, the ninth lens element 41 and the tenth lens element 42 form a cemented lens having a positive refractive power as a whole.

In the second lens group G2, the fifth lens 50 includes seven lens elements 51,52,53,54,55,56,57. The fourteenth lens element 51 is a liquid lens, and is a focal length variable lens whose refractive power changes in a negative to positive range. The 15th lens element 52 has positive refractive power, the 16th lens element 53 has negative refractive power, the 17th lens element 54 has negative refractive power, and the 18th lens element 55 and the 19th lens element 56 have positive refractive power, and the 20th lens element 57 has negative refractive power. Of these, the 15th lens element 52 and the 16th lens element 53 are cemented lenses, the 17th lens element 54 and the 18th lens element 55 are cemented lenses, and the 19th lens element 56 and the 20th lens element 56 are cemented lenses. The lens element 57 is a cemented lens. The protective glass 73j arranged on the light exit side of the twentieth lens element 57 and the filter 70f is flat glass that protects the light detection surface of the image sensor 73. As shown in FIG.

As described above, the second lens group G2 is a combination of the third lens 30 having positive refractive power, the fourth lens 40 having positive refractive power, and the fifth lens 50 having positive refractive power. and has a positive refractive power as a whole. In addition, the front portions of the first lens group G1 and the second lens group G2 (that is, the third lens 30 and the fourth lens 40) have positive refractive power as a whole. Here, the front portion of the second lens group G2, that is, the front portion combining the third lens 30 and the fourth lens 40 is telecentric to the front, and the rear focal position of this front portion is the position of the iris diaphragm 70d. It has become. Since the front portion consisting of the third lens 30 and the fourth lens 40 is telecentric on the front side, the decentering of the second lens group G2 with respect to the first lens group G1 is relatively allowed, and the optical system has relatively high reliability. can be a system.

FIG. 2 is a side sectional view enlarging the vicinity of the boundary between the first lens group G1 and the second lens group G2. Since the first lens group G1 is telecentric on the rear side and the front part of the second lens group G2 is telecentric on the front side, the fifth lens element 22 constituting the second lens 20 of the first lens group G1 is projected. A light beam relatively parallel to the optical axis OA is emitted from the surface 22b. relatively parallel rays are incident on the As a result, even if the optical axis OA of the second lens group G2 shifts in the direction perpendicular to the optical axis OA with respect to the optical axis OA of the first lens group G1, even if the optical axis OA is near the optical axis OA. Since the state of incidence of the light rays on the incident surface 31a is substantially maintained even if the distance from the optical axis OA is maintained, aberrations are unlikely to occur, and the distance between the second lens group G2 and the first lens group G1 approaches and separates. Even if misalignment occurs, aberrations are less likely to occur and performance deterioration is less likely to occur, so the optical system is less likely to be affected by assembly errors.

Returning to FIG. 1, the iris diaphragm 70d can be driven by the rear element driving section 82 to change the aperture diameter. The post-element drive section 82 operates under the control of the control device 90 that constitutes the accessory device 100b, but can also be operated manually by the user via an operation section (not shown). On the other hand, the fourteenth lens element 51 of the fifth lens 50 can be driven by the rear-stage element driving section 82 to change the focal length. A fourteenth lens element 51, which is a liquid lens, is arranged on the image side of the iris diaphragm 70d and in the vicinity of the iris diaphragm 70d. By arranging the fourteenth lens element (liquid lens) 51 next to the image side of the iris diaphragm 70d in this way, even if the refractive power of the fourteenth lens element 51 is changed, the function of the iris diaphragm 70d is not affected. become difficult. If the fourteenth lens element (liquid lens) 51 is placed on the object side of the iris diaphragm 70d, changing the refractive power of the fourteenth lens element 51 will change the state of incidence of light rays on the iris diaphragm 70d. There is a possibility that the adjustment of the aperture diameter by the diaphragm 70d is hindered.

The deflecting mirror 71 is driven by the mirror driving section 81 to change the tilt angle and the tilt direction with respect to the optical axis. The mirror driving section 81 has a motor and an encoder, and operates under the control of a control device 90 that constitutes the accessory device 100b. Specifically, the mirror driver 81 has a two-axis rotation mechanism, and rotates the deflection mirror 71 within a range of ±several tens of degrees based on the state in which the deflection mirror 71 is tilted at 45° with respect to the optical axis OA. The tilt angle can be changed, and the orientation of the deflection mirror 71 around the optical axis OA can be changed by 360°. In other words, the deflecting mirror 71 can freely change its posture, and can perform two-dimensional scanning and can move the field of view to follow the object to be photographed. Note that the mirror drive unit 81 is not essential, and the user may manually tilt or rotate the deflection mirror 71 .

The deflection mirror 71 is arranged at the front focal position of the first lens group G1, that is, at the position of the entrance pupil P1. Since the deflection mirror 71 is arranged at the position of the entrance pupil P1 of the first lens group G1, the size and weight of the deflection mirror 71 can be reduced. The position of the entrance pupil P1 where the deflection mirror 71 is arranged is conjugate with the position of the iris diaphragm 70d, which is an aperture diaphragm arranged between the fourth lens 40 and the fifth lens 50 of the second lens group G2. there is

A prism mirror 72 is arranged between the first lens group G1 and the deflection mirror 71 to combine the optical paths. Here, the photographing light LO travels straight through the semi-transmissive surface 72 a of the prism mirror 72 . On the other hand, the illumination light LI from the illumination device 75 constituting the accessory device 100b is reflected by the semi-transmissive surface 72a of the prism mirror 72 and guided to the optical path of the imaging optical system 100a. In other words, the combination of the prism mirror 72 and the illumination device 75 constitutes a coaxial illumination device. The illumination device 75 is a Koehler illumination system having a visible light source, although detailed description is omitted.

The image sensor 73 is a CMOS sensor or other semiconductor device. The image sensor 73 is driven by the sensor driving section 83 to convert the image projected onto the detection surface IP2 into an electrical signal. The position of the detection plane IP2 is conjugate with the position of the primary imaging plane IP1, and is also conjugate with the position of the object to be photographed.

The accessory device 100 b includes a mirror driving section 81 , a post-element driving section 82 , a sensor driving section 83 and a control device 90 . The control device 90 centrally controls the operations of the mirror driving section 81 , the post-element driving section 82 , and the sensor driving section 83 . As a result, it is possible to perform in-focus photographing while moving the field of view following the movement of the object.

The imaging optical system 100a of the embodiment described above includes, in order from the front side corresponding to the object side, a deflection mirror 71, a first lens group G1, and a second lens group G2. The first lens group G1 is arranged at the position of the entrance pupil P1 of the lens group G1. An iris diaphragm 70d is arranged at the position where the deflection mirror 71 and the iris diaphragm 70d are conjugate. In this imaging optical system 100a, the deflecting mirror 71 is arranged at the position of the entrance pupil P1 of the first lens group G1, so that the deflecting mirror 71 can be made smaller and lighter. Furthermore, since the deflecting mirror 71 and the iris diaphragm 70d in the second lens group G2 are arranged at conjugate positions, it is possible to prevent the occurrence of a missing field of view.

〔Example〕
Table 1 below shows data on lens surfaces and the like for the examples of the image pickup optical system according to the present invention. In Table 1 below, the radius of curvature is represented by "R", the axial distance is represented by "D", the effective radius is represented by "EA", and the refractive index for the d-line of the lens material is represented by "Nd ”. "1.00E+18" means infinity.
[Table 1]

In this imaging optical system, the combined focal length f of the first lens 10 including the lens elements 11, 12 and 13 and the second lens 20 including the lens elements 21 and 22 is 63 mm. Also, the focal length f of the third lens 30 including the lens elements 31, 32, and 33 is 50 mm. The focal length f of the fourth lens 40 including the lens elements 41, 42, 43, 44, 45 is 150 mm. Furthermore, the combined focal length f of the lens elements 52, 53, 54, 55, 56, and 57, which are the remainder of the fifth lens 50 after removing the liquid lens, is 33 mm.

Although the imaging optical system and the like have been described above according to the embodiments, the imaging optical system according to the present invention is not limited to the above-described embodiments or examples, and various modifications are possible.

For example, the fourteenth lens element 51 is not limited to a liquid lens, and can be replaced with a single lens having a refractive index Nd of 1.5 or less.

The illumination device 75 is not essential and can be replaced with various illumination systems other than coaxial illumination.

In the above embodiment, in the prism mirror 72, the optical path of the illumination light LI is bent by the semi-transmissive surface 72a, but it is also possible to bend the optical path of the photographing light LO by the semi-transmissive surface 72a so that the illumination light LI is transmitted and travels straight. . In this case, a deflecting mirror 71 is arranged in front of the optical path of the bent photographing light LO.

The first lens group G1 and the second lens group G2 need not be integral, and the first lens group G1 or the second lens group G2 can be exchangeable, and some of them can be exchangeable. can also

DESCRIPTION OF SYMBOLS 10... 1st lens, 11, 12, 13... Lens element, 20... 2nd lens, 21, 22... Lens element, 30... 3rd lens, 31, 32, 33... Lens element, 40... 4th lens, 41 , 42, 43, 44, 45... Lens element 50... Fifth lens 51, 52, 53, 54, 55, 56, 57... Lens element 70... Main body optical system 71... Deflection mirror 72... Prism mirror , 72a... Semi-transmissive surface 73... Image sensor 75... Illuminating device 90... Control device 100... Imaging device 100a... Imaging optical system 100b... Accessory device G1... First lens group G2... Second lens Group, IP1... Primary image plane, IP2... Detection plane, LI... Illumination light, LO... Photographing light, OA... Optical axis, P1... Entrance pupil

Claims (8)

A deflection mirror, a first lens group, and a second lens group are provided in order from the front side corresponding to the object side,
The deflection mirror is arranged at the position of the entrance pupil of the first lens group,
The first lens group has a primary imaging plane conjugate with the detection plane between the first lens group and the second lens group,
disposing an iris diaphragm in the second lens group;
An imaging optical system, wherein the deflecting mirror and the iris diaphragm are arranged at conjugate positions. 2. The imaging optical system according to claim 1, wherein said first lens group is telecentric on the rear side, and said deflection mirror is arranged at a front focal position of said first lens group. 3. The image pickup optical system according to claim 2, wherein said second lens group is telecentric on the front side, and said iris diaphragm is arranged at a back focal position in a portion of said second lens group further to the front than said iris diaphragm. 4. The imaging optical system according to claim 1, comprising a liquid lens on the image side of said iris diaphragm. 5. The imaging optical system according to claim 4, wherein said liquid lens has refractive power that varies in a negative to positive range. The first lens group is a combination of a lens having positive refractive power and a lens having negative refractive power,
6. The imaging optical system according to any one of claims 1 to 5, wherein the lens up to the iris diaphragm in the second lens group is a combination of a plurality of lenses having positive refractive power. A first lens group and a second lens group are provided in order from the front side, which is the object side,
The first lens group has an entrance pupil closer to the object side than the first lens group, and has a primary imaging plane conjugate with the detection plane between the second lens group and the first lens group,
disposing an iris diaphragm in the second lens group;
The imaging optical system, wherein the entrance pupil and the iris diaphragm of the first lens group are arranged at conjugate positions. 8. The imaging optical system according to claim 7, further comprising a deflecting mirror arranged at the entrance pupil position of the first lens group.

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