CN-122029471-A - Imaging optical system and image pickup apparatus having the same

Abstract

[ Problem ] to provide an imaging optical system having a small size, a large aperture, and high optical performance. [ solution ] an imaging optical system according to the present invention includes an aperture stop, and a first transflective surface, a quarter wave plate, and a second transflective surface that are arranged in order from an object side to an image side. Light from the object side sequentially passes through the first transflective surface and the quarter wave plate, is reflected by the second transflective surface toward the object side, passes through the quarter wave plate, is reflected by the first transflective surface toward the image side, and sequentially passes through the quarter wave plate and the second transflective surface toward the image plane. The total optical length, the distance on the optical axis from the first transmissive and reflective surface to the image plane, the aperture stop diameter, and the distance on the optical axis from the aperture stop to the image plane are each appropriately set.

Inventors

• ITOH DAISUKE

Assignees

• 佳能株式会社

Dates

Publication Date

20260512

Application Date

20240816

Priority Date

20231016

Claims (20)

1. 1. An imaging optical system, comprising: The maximum aperture of the light beam is set, It is characterized in that the imaging optical system sequentially comprises a first transmission and reflection surface, a quarter wave plate and a second transmission and reflection surface from the object side to the image side, Wherein light from the object side sequentially passes through the first and the quarter wave plates, is reflected by the second transflective surface toward the object side, passes through the quarter wave plate, is reflected by the first transflective surface toward the image side, and sequentially passes through the quarter wave plate and the second transflective surface toward the image plane, and Wherein the following conditional expression is satisfied: where L is the total optical length, lh is the distance on the optical axis from the first transflective surface to the image plane, D is the maximum aperture diameter, and LD is the distance on the optical axis from the maximum aperture to the image plane.
2. 2. The imaging optical system according to claim 1, wherein the maximum aperture is disposed closer to the image side than a lens disposed closest to the object among lenses included in the imaging optical system, Wherein the following conditional expression is satisfied: 。
3. 3. Imaging optical system according to claim 1 or 2, characterized in that the first and second transflector surfaces are arranged closer to the image plane than the maximum aperture.
4. 4. The imaging optical system according to any one of claims 1 to 3, characterized in that the following conditional expression is satisfied: Wherein the method comprises the steps of Is the angle of the outermost off-axis ray passing through the center of the maximum aperture and entering the first transflective surface with respect to the optical axis, and Is the angle of the outermost off-axis ray with respect to the optical axis after being reflected by the second transflector surface and by the first transflector surface.
5. 5. The imaging optical system according to any one of claims 1 to 4, characterized in that the second transflective surface is disposed adjacent to the first transflective surface and closer to an image plane than the first transflective surface, Wherein the following conditional expression is satisfied: where fP is a focal length of a structure surrounded by the first and second transflective surfaces, and f is a focal length of the imaging optical system.
6. 6. The imaging optical system according to any one of claims 1 to 5, characterized in that a space between the first and second transflective surfaces is filled with a material other than air, Wherein the following conditional expression is satisfied: where nd is the refractive index of the material.
7. 7. The imaging optical system according to any one of claims 1 to 6, characterized in that the following conditional expression is satisfied: Wherein Li is the distance on the optical axis from the second transflective surface to the image plane.
8. 8. The imaging optical system according to any one of claims 1 to 7, characterized in that the second transflective surface is a lens surface of the imaging optical system disposed closest to an image plane.
9. 9. The imaging optical system according to any one of claims 1 to 8, characterized in that one of the first and second transflective surfaces is a planar surface.
10. 10. The imaging optical system according to any one of claims 1 to 9, further comprising a negative lens disposed adjacent to the first transflective surface and closer to an object than the first transflective surface, Wherein the second transflective surface is disposed adjacent to the first transflective surface and closer to the image plane than the first transflective surface, and Wherein the following conditional expression is satisfied: where fN is the focal length of the negative lens and fP is the focal length of the structure surrounded by the first and second transflective surfaces.
11. 11. The imaging optical system according to any one of claims 1 to 10, further comprising a negative lens disposed adjacent to the first transflective surface and closer to an object than the first transflective surface, Characterized in that the following conditional expression is satisfied: Where fN is the focal length of the negative lens, and f is the focal length of the imaging optical system.
12. 12. The imaging optical system according to any one of claims 1 to 11, further comprising a negative lens disposed adjacent to the first transflective surface and closer to an object than the first transflective surface, Characterized in that the following conditional expression is satisfied: Wherein R1 is the radius of curvature of the object side lens surface of the negative lens and R2 is the radius of curvature of the second transflective surface.
13. 13. The imaging optical system according to any one of claims 1 to 12, further comprising a negative lens disposed adjacent to the first transflective surface and closer to an object than the first transflective surface, Characterized in that the following conditional expression is satisfied: where fF is a focal length from an object side lens surface of the negative lens to the second transflective surface, and f is a focal length of the imaging optical system.
14. 14. The imaging optical system according to any one of claims 1 to 13, further comprising a negative lens disposed adjacent to the first transflective surface and closer to an object than the first transflective surface, Characterized in that the space between the first and the second transflective surface is filled with a material other than air, Wherein the following conditional expression is satisfied: where nd is the refractive index of the material and ndN is the refractive index of the negative lens.
15. 15. The imaging optical system according to any one of claims 1 to 14, further comprising a negative lens disposed adjacent to the first transflective surface and closer to an object than the first transflective surface, Characterized in that the following conditional expression is satisfied: Where d is the distance on the optical axis from the object side lens surface of the negative lens to the second transflective surface.
16. 16. The imaging optical system according to any one of claims 1 to 15, further comprising a negative lens disposed adjacent to the first transflective surface and closer to an object than the first transflective surface, Characterized in that there is no air gap between the object side lens surface of the negative lens and the second transflective surface.
17. 17. The imaging optical system according to any one of claims 1 to 16, characterized in that the following conditional expression is satisfied: where f is the focal length of the imaging optical system.
18. 18. The imaging optical system according to any one of claims 1 to 17, characterized in that the following conditional expression is satisfied: where Oe is the outer diameter of the lens disposed closest to the object, and Ie is the outer diameter of the lens disposed closest to the image plane.
19. 19. The imaging optical system according to any one of claims 1 to 18, characterized in that one of the first and second transflective surfaces is a surface configured to separate incident light into reflected light and transmitted light according to a polarization state.
20. 20. The imaging optical system according to claim 19, wherein the other of the first and second transflective surfaces is a surface of a half mirror or a cholesteric liquid crystal.

Description

Imaging optical system and image pickup apparatus having the same Technical Field The present invention relates to an imaging optical system. Background A configuration called gaussian for realizing a large diameter lens using a small number of lenses is conventionally known. However, correction of coma halo occurring in the sagittal direction with this configuration results in significant curvature of field on the lower side. In the case where a lens having a strong negative refractive power is disposed directly in front of the image sensor to correct a significant curvature of field on the lower side, light rays passing through the negative lens will enter the image sensor at a large angle with respect to the optical axis, resulting in so-called light blocking of the image sensor and a darker image toward the edge. Recently, optical systems have been proposed that use polarization to control reflection and transmission at the lens surface. Patent document 1 discloses a configuration using surface reflection within a lens having two to three lenses. Patent document 2 discloses a configuration that utilizes surface reflection within a lens to allow switching from an imaging system to an observation system by rearranging lenses located near a reflection surface on the image side while keeping the front lens unit in common. Prior art literature Patent literature Patent document 1 Japanese patent application laid-open No. 2005-352273 Patent document 2 Japanese patent application laid-open No. 2013-218078 Disclosure of Invention Problems to be solved by the invention However, although the configuration described in patent document 1 can have a reduced size and a small number of lenses, there are difficulties in aberration correction and a large aperture specification cannot be supported. The configuration described in patent document 2 narrows the light beam from an on-axis position to an outermost off-axis ray to accommodate the observation system, and it becomes difficult to support a large aperture specification with the configured lens diameter. The total lens length is long and the distance from the lens closest to the object to the aperture stop is large, resulting in a very large lens diameter of the lens closest to the object. An object of the present invention is to provide an imaging optical system having a reduced size, a large aperture, and high optical performance. Means for solving the problems An imaging optical system according to an aspect of the present invention includes a maximum aperture, and further includes, in order from an object side to an image side, a first transflective surface, a quarter wave plate, and a second transflective surface. Light from the object side sequentially passes through the first transflector and the quarter wave plate, is reflected by the second transflector toward the object side, passes through the quarter wave plate, is reflected by the first transflector toward the image side, and sequentially passes through the quarter wave plate and the second transflector toward the image plane. The following conditional expression is satisfied: Where L is the total optical length, lh is the distance on the optical axis from the first transflective surface to the image plane, D is the maximum aperture diameter, and LD is the distance on the optical axis from the maximum aperture to the image plane. Effects of the invention The present invention can provide an imaging optical system having a reduced size, a large aperture, and high optical performance. Drawings Fig. 1 is a schematic diagram illustrating an optical path of an optical system. Fig. 2 is a schematic diagram illustrating an optical path of the optical system. Fig. 3 is a sectional view of an imaging optical system according to example 1. Fig. 4 is an aberration diagram in an in-focus state at infinity of the imaging optical system according to example 1. Fig. 5 is a cross-sectional view of an imaging optical system according to example 2. Fig. 6 is an aberration diagram in an in-focus state of the imaging optical system according to example 2 at infinity. Fig. 7 is a cross-sectional view of an imaging optical system according to example 3. Fig. 8 is an aberration diagram in an in-focus state at infinity of the imaging optical system according to example 3. Fig. 9 is a cross-sectional view of an imaging optical system according to example 4. Fig. 10 is an aberration diagram in an in-focus state of the imaging optical system according to example 4 at infinity. Fig. 11 is a sectional view of an imaging optical system according to example 5. Fig. 12 is an aberration diagram in an in-focus state at infinity of the imaging optical system according to example 5. Fig. 13 is a sectional view of an imaging optical system according to example 6. Fig. 14 is an aberration diagram in an in-focus state of the imaging optical system according to example 6 at infinity. Fig. 15 is a sectional view of an imaging optical system ac