Prism optical system

• US 5,991,103 A
• Filed: 09/12/1997
• Issued: 11/23/1999
• Est. Priority Date: 10/21/1994
• Status: Expired due to Term

• Current Assignee: Olympus Optical Company Ltd. (Olympus Corporation)
• Original Assignee: Olympus Optical Company Ltd. (Olympus Corporation)
• Inventors: Togino, Takayoshi
• Primary Examiner(s): Shafer, Ricky D.
• Application Number:
  US08/928,406
• Time in Patent Office: 802 Days
• Field of Search: 359/834, 359/835, 359/836, 359/629, 359/634, 359/631, 359/633, 354/219, 354/224, 354/225, 396/373, 396/384, 396/FOR 859, 348/341, 345/7, 345/8
• US Class Current: 359/834
• CPC Class Codes: G02B 17/045 having static image erecting or reversing properties only optical derotators G02B27/642; optical devices for controlling the direction of light using movable or deformable optical elements G02B26/08
• CPC Class Codes: G02B 17/0816 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: G02B 25/001 Eyepieces

Abstract

A prism optical system for use as an ocular optical system of a visual display apparatus, which has a compact size as a whole, causes a minimal reduction of the light intensity in the ocular optical system, provides a wide field angle and a large exit pupil diameter, and is effectively corrected for off-axis aberrations. The prism optical system has two transparent surfaces (6 and 7), and two reflecting surfaces (2 and 3). The space between the first transparent surface (6) and the second transparent surface (7) is filled with a medium having a refractive index not smaller than 1.3. Assuming that a light ray which emanates from the center of an image surface (1) and is perpendicularly incident on a pupil position (5) is defined as a chief ray, the two reflecting surfaces (2 and 3) are disposed such that both the reflecting surfaces are tilted with respect to the chief ray, and that the two reflecting surfaces (2and 3) are tilted relative to each other so as to diverge toward the image surface (1) or the pupil position (5) in a plane in which the optical axis bends. At the same time, the two reflecting surfaces (2 and 3) are disposed so that a light ray emanating from the image surface (1) approximately intersects a light ray which emanates from the second transparent surface (7) and enters the pupil position (5).

Claims

1. A prism optical system comprising, in order from an image surface side along an optical path:

a first transparent surface;

a concave first reflecting surface;

a second reflecting surface; and

a second transparent surface;

said first transparent surface, said first reflecting surface, said second reflecting surface, and said second transparent surface are disposed so that the four surfaces form surrounding surfaces of a single prism that face each other across said medium;

a space between said first transparent surface, which is disposed at said image surface side, and said second transparent surface, which is disposed at a pupil side of said prism optical system, being filled with a medium having a refractive index not less than 1.3;

the concavity of said first reflecting surface facing said medium;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of an image surface of said prism optical system, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image surface of said prism optical system and said pupil position in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image surface of said prism optical system approximately intersects a light ray emanating from said second transparent surface and enters said pupil position; and

an angle θ

between said chief ray and a line normal to at least one of said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">12.5°

<

θ

<

32.5°

.

7. A prism optical system accord to any one of claims 1, 2, 3 or 4, wherein:

at least one of said first reflecting surface and said second reflecting surface is a toric surface.

8. A prism optical system according to claim 1, or 2, further comprising:

an imaging device disposed at a position of said image surface of said prism optical system.

9. A prism optical system according to any one of claims 1, 2, 3 or 4, wherein:

both said first reflecting surface and said second reflecting surface are reflecting surfaces having positive power.

10. A prism optical system according to any one of claims 1, 2, 3 or 4, wherein:

both said first reflecting surface and said second reflecting surface are toric surfaces.

11. A prism optical system according to any one of claims 1, 2, 3 or 4, wherein:

said second reflecting surface is a semitransparent surface.

12. A prism optical system according to claim 11, wherein:

said semitransparent surface has a transmittance of from 20% to 80%.

17. A prism optical system according to claim 1, wherein:

a relative tilt angle φ

between said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">35°

<

φ

<

55°

.

18. A prism optical system according to claim 1, wherein:

a relative tilt angle φ

between said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">40°

<

φ

<

50°

.

19. A prism optical system according to claim 1 or 2, further comprising:

a photosensitive material disposed at a position of said image surface of said prism optical system.

20. A prism optical system according to claim 1 or 2, wherein said second reflecting surface has a curved surface configuration providing one of converging and diverging power to a light beam.

2. A prism optical system comprising, in order from an image surface side along an optical path:

a first transparent surface;

a concave first reflecting surface;

a second reflecting surface; and

a second transparent surface;

a space between said first transparent surface, which is disposed at said image surface side, and said second transparent surface, which is disposed at a pupil side of said prism optical system, being filled with a medium having a refractive index not less than 1.3;

said first transparent surface, said first reflecting surface, said second reflecting surface, and said second transparent surface are disposed so that the four surfaces form surrounding surfaces of a single prism that face each other across said medium, the concavity of said first reflecting surface facing said medium;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of an image surface of said prism optical system, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image surface of said prism optical system and said pupil position in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image surface of said prism optical system approximately intersects a light ray emanating from said second transparent surface and enters said pupil position; and

a relative tilt angle φ

between said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">35°

<

φ

<

55°

.

13. A prism optical system according to claim 2, wherein:

an angle θ

between said chief ray and a line normal to at least one of said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">12.5°

<

θ

<

32.5°

.

14. A prism optical system according to claim 13, wherein:

said condition is satisfied for said angle θ

between said chief ray and a line normal to each of said first reflecting surface and said second reflecting surface.

15. A prism optical system according to claim 2, wherein:

an angle θ

between said chief ray and a line normal to at least one of said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">θ

=22.5°

.

16.

16. A prism optical system according to claim 15, wherein:

said condition is satisfied for said angle θ

between said chief ray and a line normal to each of said first reflecting surface and said second reflecting surface.

3. A prism optical system for use as an ocular optical system of a visual display apparatus, said prism optical system comprising:

an image forming means for observation, said image forming means being locatable in front of an observer'"'"'s face; and

an ocular optical system for projecting an image of said image forming means in air as an enlarged image, said ocular optical system comprising, in order from an image forming means side;

a first transparent surface disposed in opposition to said image forming means,

a first reflecting surface,

a second reflecting surface, and

a second transparent surface,

a space between said first transparent surface, which is disposed at said image forming means side of said ocular optical system, and said second transparent surface, which is disposed at an observer'"'"'s eyeball side of said ocular optical system, being filled with a medium having a refractive index not less than 1.3;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of said image forming means, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system; and

said first transparent surface, said first reflecting surface, said second reflecting surface, and said second transparent surface are disposed so that the four surfaces form surrounding surfaces of a single prism that face each other across said medium;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image forming means and an observer'"'"'s eyeball in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image forming means approximately intersects a light ray emanating from said ocular optical system and enters said observer'"'"'s eyeball; and

an angle θ

between said chief ray and a line normal to at least one of said first reflecting surface and said second reflecting surface satisfying the following condition;

space="preserve" listing-type="equation">12.5°

<

θ

<

32.5°

,

wherein

at least one of said first reflecting surface and said second reflecting surface is a reflecting surface having positive power.

21. A prism optical system according to claim 3 or 4, wherein said first reflecting surface has a positive power, and said second reflecting surface has a curved surface configuration providing one of converging and diverging power to a light beam.

22. A prism optical system according to claim, 3 or 4, wherein said second reflecting surface has a positive power, and said first reflecting surface has a curved surface configuration providing one of converging and diverging a power to a light beam.

4. A prism optical system for use as an ocular optical system of a visual display apparatus, said prism optical system comprising:

an image forming means for observation, said image forming means being locatable in front of an observer'"'"'s face; and

an ocular optical system for projecting an image of said image forming means in air as an enlarged image, said ocular optical system comprising, in order from an image forming means side;

a first transparent surface disposed in opposition to said image forming means,

a first reflecting surface,

a second reflecting surface, and

a second transparent surface,

a space between said first transparent surface, which is disposed at said image forming means side of said ocular optical system, and said second transparent surface, which is disposed at an observer'"'"'s eyeball side of said ocular optical system, being filled with a medium having a refractive index not less than 1.3;

said first transparent surface, said first reflecting surface, said second reflecting surface, and said second transparent surface are disposed so that the four surfaces form surrounding surfaces of a single prism that face each other across said medium,

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of said image forming means, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system; and

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image forming means and an observer'"'"'s eyeball in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image forming means approximately intersects a light ray emanating from said ocular optical system and enters said observer'"'"'s eyeball; and

a relative tilt angle φ

between said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">35°

<

φ

<

55°

wherein at least one of said first reflecting surface and said second reflecting surface is a reflecting surface having positive power.

5. A prism optical system for use as an ocular optical system of a visual display apparatus, said prism optical system comprising:

an image forming means for observation, said image forming means being locatable in front of an observer'"'"'s face;

an ocular optical system for projecting an image of said image forming means in air as an enlarged image, said ocular optical system comprising, in order from an image forming means side;

a first transparent surface disposed in opposition to said image forming means,

a first reflecting surface,

a second reflecting surface, and

a second transparent surface,

a space between said first transparent surface, which is disposed at said image forming means side of said ocular optical system, and said second transparent surface, which is disposed at an observer'"'"'s eyeball side of said ocular optical system, being filled with a medium having a refractive index not less than 1.3;

said first transparent surface, said first reflecting surface, said second reflecting surface, and said second transparent surface are disposed so that the four surfaces form surrounding surfaces of a single prism that face each other across said medium, and

support means for positioning a pair of said ocular optical system with respect to each other,

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of said image forming means, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image forming means and an observer'"'"'s eyeball in a plane in which an optical axis of said prism optical system bends,

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image forming means approximately intersects a light ray emanating from said ocular optical system and enters said observer'"'"'s eyeball, and

an angle θ

between said chief ray and a line normal to at least one of said first reflecting surface and said second reflecting surface satisfying the following condition;

space="preserve" listing-type="equation">12.5°

<

θ

<

32.5°

.

23. A prism optical system according to claim 5 or 6, further comprising:

means for supporting a pair of said ocular optical system on an observer'"'"'s head.

24. A prism optical system according to claim 5 or 6, wherein both said first reflecting surface and said second reflecting surface have a curved surface configuration providing one of converging and diverging a power to a light beam.

6. A prism optical system for use as an ocular optical system of a visual display apparatus, said prism optical system comprising:

an image forming means for observation, an image forming means being locatable in front of an observer'"'"'s face;

an ocular optical system for projecting an image of said image forming means in air as an enlarged image, said ocular optical system comprising, in order from an image forming means side;

a first transparent surface disposed in opposition to said image forming means,

a first reflecting surface,

a second reflecting surface, and

a second transparent surface,

a space between said first transparent surface, which is disposed at said image forming means side of said ocular optical system, and said second transparent surface, which is disposed at an observer'"'"'s eyeball side of said ocular optical system, being filled with a medium having a refractive index not less than 1.3;

said first transparent surface, said first reflecting surface, said second reflecting surface, and said second transparent surface are disposed so that the four surfaces form surrounding surfaces of a single prism that face each other across said medium; and

support means for positioning a pair of said ocular optical system with respect to each other,

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of said image forming means, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system, and

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image forming means and an observer'"'"'s eyeball in a plane in which an optical axis of said prism optical system bends,

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image forming means approximately intersects a light ray emanating from said ocular optical system and enters said observer'"'"'s eyeball, and

a relative tilt angle φ

between said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">35°

<

φ

<

55°

.

25. A prism optical system comprising, in order from an image surface side along an optical path:

a first transparent surface;

a concave first reflecting surface;

a second reflecting surface; and

a second transparent surface;

a space between said first transparent surface, which is disposed at said image surface side, and said second transparent surface, which is disposed at a pupil side of said prism optical system, being filled with a medium having a refractive index not less than 1.3;

the concavity of said first reflecting surface facing said medium;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of an image surface of said prism optical system, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image surface of said prism optical system and said pupil position in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image surface of said prism optical system approximately intersects a light ray emanating from said second transparent surface and enters said pupil position; and

an angle θ

between said chief ray and a line normal to at least one of said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">12.5°

<

θ

<

32.5°

,

wherein both said first reflecting surface and said second reflecting surface are reflecting surfaces having positive power.

26. A prism optical system comprising, in order from an image surface side along an optical path:

a first transparent surface;

a concave first reflecting surface;

a second reflecting surface; and

a second transparent surface;

a space between said first transparent surface, which is disposed at said image surface side, and said second transparent surface, which is disposed at a pupil side of said prism optical system, being filled with a medium having a refractive index not less than 1.3;

the concavity of said first reflecting surface facing said medium;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of an image surface of said prism optical system, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image surface of said prism optical system and said pupil position in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image surface of said prism optical system approximately intersects a light ray emanating from said second transparent surface and enters said pupil position; and

a relative tilt angle φ

between said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">35°

<

φ

<

55°

,

wherein both said first reflecting surface and said second reflecting surface are reflecting surfaces having positive power.

27. A prism optical system for use as an ocular optical system of a visual display apparatus, said prism optical system comprising:

an image forming means for observation, said image forming means being locatable in front of an observer'"'"'s face; and

an ocular optical system for projecting an image of said image forming means in air as an enlarged image, said ocular optical system comprising, in order from an image forming means side;

a first transparent surface disposed in opposition to said image forming means,

a first reflecting surface,

a second reflecting surface, and

a second transparent surface,

a space between said first transparent surface, which is disposed at said image forming means side of said ocular optical system, and said second transparent surface, which is disposed at an observer'"'"'s eyeball side of said ocular optical system, being filled with a medium having a refractive index not less than 1.3;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of said image forming means, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image forming means and an observer'"'"'s eyeball in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image forming means approximately intersects a light ray emanating from said ocular optical system and enters said observer'"'"'s eyeball; and

an angle θ

between said chief ray and a line normal to at least one of said first reflecting surface and said second reflecting surface satisfying the following condition;

space="preserve" listing-type="equation">12.5°

<

θ

<

32.5°

,

wherein at least one of said first reflecting surface and said second reflecting surface is a reflecting surface having positive power, and

both said first reflecting surface and said second reflecting surface are reflecting surfaces having positive power.

28. A prism optical system for use as an ocular optical system of a visual display apparatus, said prism optical system comprising:

an image forming means for observation, said image forming means being locatable in front of an observer'"'"'s face; and

an ocular optical system for projecting an image of said image forming means in air as an enlarged image, said ocular optical system comprising, in order from an image forming means side;

a first transparent surface disposed in opposition to said image forming means,

a first reflecting surface,

a second reflecting surface, and

a second transparent surface,

a space between said first transparent surface, which is disposed at said image forming means side of said ocular optical system, and said second transparent surface, which is disposed at an observer'"'"'s eyeball side of said ocular optical system, being filled with a medium having a refractive index not less than 1.3;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of said image forming means, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image forming means and an observer'"'"'s eyeball in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image forming means approximately intersects a light ray emanating from said ocular optical system and enters said observer'"'"'s eyeball; and

a relative tilt angle φ

between said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">35°

<

φ

<

55°

wherein at least one of said first reflecting surface and said second reflecting surface is a reflecting surface having positive power, and both said first reflecting surface and said second reflecting surface are reflecting surfaces having positive power.

29. A prism optical system comprising, in order from an image surface side along an optical path:

a first transparent surface;

a concave first reflecting surface;

a second reflecting surface; and

a second transparent surface;

a space between said first transparent surface, which is disposed at said image surface side, and said second transparent surface, which is disposed at a pupil side of said prism optical system, being filled with a medium having a refractive index not less than 1.3;

the concavity of said first reflecting surface facing said medium;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of an image surface of said prism optical system, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image surface of said prism optical system and said pupil position in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image surface of said prism optical system approximately intersects a light ray emanating from said second transparent surface and enters said pupil position; and

an angle θ

between said chief ray and a line normal to at least one of said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">12.5°

<

θ

<

32.5°

,

wherein both said first reflecting surface and said second reflecting surface are toric surfaces.

30. A prism optical system comprising, in order from an image surface side along an optical path:

a first transparent surface;

a concave first reflecting surface;

a second reflecting surface; and

a second transparent surface;

a space between said first transparent surface, which is disposed at said image surface side, and said second transparent surface, which is disposed at a pupil side of said prism optical system, being filled with a medium having a refractive index not less than 1.3;

the concavity of said first reflecting surface facing said medium;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of an image surface of said prism optical system, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image surface of said prism optical system and said pupil position in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image surface of said prism optical system approximately intersects a light ray emanating from said second transparent surface and enters said pupil position; and

a relative tilt angle φ

between said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">35°

<

φ

<

55°

,

wherein both said first reflecting surface and said second reflecting surface are toric surfaces.

31. A prism optical system for use as an ocular optical system of a visual display apparatus, said prism optical system comprising:

an image forming means for observation, said image forming means being locatable in front of an observer'"'"'s face; and

an ocular optical system for projecting an image of said image forming means in air as an enlarged image, said ocular optical system comprising, in order from an image forming means side;

a first transparent surface disposed in opposition to said image forming means,

a first reflecting surface,

a second reflecting surface, and

a second transparent surface,

a space between said first transparent surface, which is disposed at said image forming means side of said ocular optical system, and said second transparent surface, which is disposed at an observer'"'"'s eyeball side of said ocular optical system, being filled with a medium having a refractive index not less than 1.3;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of said image forming means, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system;

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image forming means and an observer'"'"'s eyeball in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image forming means approximately intersects a light ray emanating from said ocular optical system and enters said observer'"'"'s eyeball; and

an angle θ

between said chief ray and a line normal to at least one of said first reflecting surface and said second reflecting surface satisfying the following condition;

space="preserve" listing-type="equation">12.5°

<

θ

<

32.5°

,

wherein at least one of said first reflecting surface and said second reflecting surface is a reflecting surface having positive power, and both said first reflecting surface and said second reflecting surface are toric surfaces.

32. A prism optical system for use as an ocular optical system of a visual display apparatus, said prism optical system comprising:

an image forming means for observation, said image forming means being locatable in front of an observer'"'"'s face; and

an ocular optical system for projecting an image of said image forming means in air as an enlarged image, said ocular optical system comprising, in order from an image forming means side;

a first transparent surface disposed in opposition to said image forming means,

a first reflecting surface,

a second reflecting surface, and

a second transparent surface,

a space between said first transparent surface, which is disposed at said image forming means side of said ocular optical system, and said second transparent surface, which is disposed at an observer'"'"'s eyeball side of said ocular optical system, being filled with a medium having a refractive index not less than 1.3;

said first reflecting surface and said second reflecting surface being tilted with respect to a chief ray, said chief ray being a light ray which emanates from a center of said image forming means, which is reflected by said first reflecting surface and said second reflecting surface, and which is perpendicularly incident on a pupil position of said prism optical system; and

said first reflecting surface and said second reflecting surface are tilted relative to each other so as to diverge toward at least one of said image forming means and an observer'"'"'s eyeball in a plane in which an optical axis of said prism optical system bends;

said first reflecting surface and said second reflecting surface are disposed so that a light ray emanating from said image forming means approximately intersects a light ray emanating from said ocular optical system and enters said observer'"'"'s eyeball; and

a relative tilt angle φ

between said first reflecting surface and said second reflecting surface satisfies the following condition;

space="preserve" listing-type="equation">35°

<

φ

<

55°

,

wherein at least one of said first reflecting surface and said second reflecting surface is a reflecting surface having positive power, and both said first reflecting surface and said second reflecting surface are toric surfaces.