Image-forming optical system

• US 6,788,343 B1
• Filed: 10/13/1999
• Issued: 09/07/2004
• Est. Priority Date: 12/07/1998
• Status: Expired due to Term

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Corporation
• Inventors: Togino, Takayoshi
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): NGUYEN, LUONG TRUNG
• Application Number:
  US09/417,914
• Time in Patent Office: 1,791 Days
• Field of Search: 348/335, 348/337, 348/341, 348/65, 348/68, 359/631, 359/633, 359/634, 359/637, 359/834, 359/835, 396/17, 396/384
• US Class Current: 348/341
• CPC Class Codes: G02B 17/0848 off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements
• CPC Class Codes: G02B 17/086 wherein the system is made of a single block of optical material, e.g. solid catadioptric systems
• CPC Class Codes: H04N 23/55 Optical parts specially adapted for electronic image sensors; Mounting thereof
• CPC Class Codes: H04N 23/555 for picking-up images in sites, inaccessible due to their dimensions or hazardous conditions, e.g. endoscopes or borescopes
• CPC Class Codes: H04N 23/63 by using electronic viewfinders

Abstract

A high-performance image-forming optical system made compact and thin by folding an optical path using reflecting surfaces arranged to minimize the number of reflections. The image-forming optical system has a single prism. When image-side three surfaces of the prism are defined as a surface A, a surface B and a surface C in order from the image plane side thereof, at least one of the surfaces B and C has a rotationally asymmetric curved surface configuration that gives a power to a light beam and corrects aberrations due to decentration. The optical system leads light rays from an object to the image plane without forming an image in the prism and has a pupil in the prism. The surface A is a transmitting surface through which rays exit from the prism. The surfaces B and C are internally reflecting surfaces, which are positioned to face each other to form a Z-shaped optical path.

Claims

1. An image-forming optical system having a positive refracting power as a whole for forming an object image, said image-forming optical system comprising:

at least one prism formed from a medium having a refractive index (n) larger than 1.3 (n>

1.3),

wherein said prism has at least four optical surfaces that transmit or reflect a light beam, and when image-side three surfaces of the at least four optical surfaces are defined as a surface A, a surface B and a surface C in order from an image plane side of said prism, at least one of said surface B and said surface C has a curved surface configuration that gives a power to a light beam, said curved surface configuration having a rotationally asymmetric surface configuration that corrects aberrations due to decentration,

said image-forming optical system being adapted to lead light rays from an object to an image plane without forming an image in said prism, and said image-forming optical system having a pupil in said prism,

said surface A having a transmitting action by which rays internally reflected from said surface B are allowed to exit from said prism,

said surface B having a reflecting action to reflect rays internally reflected from said surface C, and said surface C having a reflecting action.

2. An image-forming optical system according to claim 1, wherein said surface C and said surface B are positioned to face each other across said medium, thereby forming a Z-shaped optical path.

3. An image-forming optical system according to claim 1, wherein both said surface C and said surface B have a rotationally asymmetric surface configuration that gives a power to a light beam and corrects aberrations due to decentration.

4. An image-forming optical system according to claim 1, wherein the rotationally asymmetric surface configuration of at least one of said surface C and said surface B is a plane-symmetry free-form surface having only one plane of symmetry.

5. An image-forming optical system according to claim 3, wherein the rotationally asymmetric surface configurations of both said surface C and said surface B are plane-symmetry free-form surfaces each having only one plane of symmetry.

6. An image-forming optical system according to claim 5, wherein the only one plane of symmetry of the plane-symmetry free-form surface that forms said surface C and the only one plane of symmetry of the plane-symmetry free-form surface that forms said surface B are formed in a same plane.

7. An image-forming optical system according to claim 1, wherein said surface A has a rotationally asymmetric surface configuration that gives a power to a light beam and corrects aberrations due to decentration.

8. An image-forming optical system according to claim 7, wherein the rotationally asymmetric surface configuration of said surface A is a plane-symmetry free-form surface having only one plane of symmetry.

9. An image-forming optical system according to claim 1, wherein a rotationally asymmetric surface placed in an object-side part of said prism, exclusive of said surfaces A, B and C, is a plane-symmetry free-form surface having only one plane of symmetry.

10. An image-forming optical system according to claim 9, wherein the object-side part of said prism and an image-side part of said prism including said surfaces A, B and C each have at least one plane-symmetry free-form surface having only one plane of symmetry, and the only one plane of symmetry of the at least one plane-symmetry free-form surface in said object-side part and the only one plane of symmetry of the at least one plane-symmetry free-form surface in said image-side part are placed in a same plane.

11. An image-forming optical system according to claim 1, wherein said pupil is placed between an object-side part of said prism, exclusive of said surfaces A, B and C, and an image-side part of said prism including said surfaces A, B and C, and said image-side part is placed between said pupil and said image plane.

12. An image-forming optical system according to claim 11, wherein a stop is placed on said pupil.

13. An image-forming optical system according to claim 1, wherein an object-side part of said prism, exclusive of said surfaces A, B and C, has at least two reflecting surfaces each having a curved surface configuration that gives a power to a light beam.

14. An image-forming optical system according to claim 1, wherein an object-side part of said prism, exclusive of said surfaces A, B and C, comprises two optical surfaces, which are an entrance surface serving as both a reflecting surface and a transmitting surface, and a reflecting surface.

15. An image-forming optical system according to claim 1, wherein an object-side part of said prism, exclusive of said surfaces A, B and C, comprises an entrance surface having a transmitting action by which a light beam is allowed to enter said prism, and two reflecting surfaces that give a power to a light beam.

16. An image-forming optical system according to claim 15, wherein said object-side part of said prism is arranged such that said two reflecting surfaces of said object-side part are placed to face each other across said medium, and said entrance surface and said two reflecting surfaces form a Z-shaped optical path.

17. An image-forming optical system according to claim 1, wherein an object-side part of said prism, exclusive of said surfaces A, B and C, comprises three optical surfaces, which are an entrance surface serving as both a reflecting surface and a transmitting surface, and two reflecting surfaces.

18. An image-forming optical system according to any one of claims 1 to 17, wherein when a decentration direction of said image-forming optical system is a Y-axis direction, and a plane parallel to an axial principal ray is a YZ-plane, and further a direction perpendicularly intersecting the YZ-plane is an X-axis direction, at least one of the following conditions is satisfied:

19. An image-forming optical system according to any one of claims 1 to 17, wherein when a decentration direction of said image-forming optical system is a Y-axis direction, and a plane parallel to an axial principal ray is a YZ-plane, and further a direction perpendicularly intersecting the YZ-plane is an X-axis direction, at least one of the following conditions is satisfied:

20. An image-forming optical system according to any one of claims 1 to 17, wherein at least one of the following conditions is satisfied:

21. An image-forming optical system according to any one of claims 1 to 17, wherein the following conditions is satisfied:

22. An image-forming optical system according to any one of claims 13 to 17, wherein when a decentration direction of said image-forming optical system is a Y-axis direction, and a plane parallel to an axial principal ray is a YZ-plane, and further a direction perpendicularly intersecting the YZ-plane is an X-axis direction, at least one of the following conditions is satisfied:

23. An image-forming optical system according to any one of claims 13 to 17, wherein when a decentration direction of said image-forming optical system is a Y-axis direction, and a plane parallel to an axial principal ray is a YZ-plane, and further a direction perpendicularly intersecting the YZ-plane is an X-axis direction, at least one of the following conditions is satisfied:

24. A finder optical system comprising:

said image-forming optical system according to claim 1, said image-forming optical system being provided as a finder objective optical system;

an image-inverting optical system for erecting an object image formed by said finder objective optical system; and

an ocular optical system.

25. A camera apparatus comprising:

said finder optical system according to claim 24; and

an objective optical system for photography provided in parallel to said finder optical system.

26. An image pickup optical system comprising:

said image-forming optical system according to claim 1; and

an image pickup device placed in an image plane formed by said image-forming optical system.

27. A camera apparatus comprising:

said image-forming optical system according to claim 1, said image-forming optical system being provided as an objective optical system for photography; and

a finder optical system placed in one of an optical path separate from an optical path of said objective optical system for photography and an optical path split from the optical path of said objective optical system for photography.

28. An electronic camera apparatus comprising:

said image-forming optical system according to claim 1;

an image pickup device placed in an image plane formed by said image-forming optical system;

a recording medium for recording image information received by said image pickup device; and

an image display device that receives image information from one of said recording medium and said image pickup device to form an image for observation.

29. An endoscope system comprising:

an observation system having said image-forming optical system according to claim 1 and an image transmitting member for transmitting an image formed by said image-forming optical system along a longitudinal axis; and

an illumination system having an illuminating light source and an illuminating light transmitting member for transmitting illuminating light from said illuminating light source along said longitudinal axis.