Method and apparatus for image enhancement and aberration corrections in a small real image projection system, using an off-axis reflector, neutral density window, and an aspheric corrected surface of revolution

• US 20030043345A1
• Filed: 09/05/2001
• Published: 03/06/2003
• Est. Priority Date: 09/05/2001
• Status: Active Grant

• Current Assignee: Optical Products Development Corporation
• Original Assignee: Douglas L. Robinson, Kenneth S. Westort
• Inventors: Westort, Kenneth S., Robinson, Douglas L.
• Granted Patent: US 6,598,976 B2
• Time in Patent Office: Days
• US Class Current: 353/20
• CPC Class Codes: G02B 17/08 Catadioptric systems used in non-imaging applications G02B19/00
• CPC Class Codes: G02B 17/0856 comprising a refractive element with a reflective surface, the reflection taking place inside the element, e.g. Mangin mirrors
• CPC Class Codes: G02B 27/0018 with means for preventing ghost images anti-reflection coatings G02B1/11
• CPC Class Codes: G02B 30/56 by projecting aerial or floating images
• CPC Class Codes: G07F 9/02 Devices for alarm or indication, e.g. when empty; Advertising arrangements in coin-freed apparatus alarms or warning devices indicating the interruption of flow to be metered G07F15/10

Abstract

A real image projection system comprises a single curved mirror having two different optical surfaces of revolution, one on the convex surface and one on the concave surface. In one embodiment, the convex surface is a conical curve of spherical or parabolic surface of revolution, coated with a reflective optical coating. The concave surface is much like that of a Mangin mirror, but it has an aspheric surface of revolution, optimized to reduce spherical aberrations over a larger area offset from the optical axis. The system optionally employs a single aspheric surface of revolution on the concave surface for reduction of aberrations, although the Mangin mirror approach, using an aspheric concave surface of revolution, is the preferred embodiment.

Claims

1. A real image projection system, comprising:

a) an injection molded acrylic mirror of two different surfaces of revolution, mounted with an optical axis of said mirror at a tilted angle relative to an optical axis of said system; and

b) a neutral density window or beamsplitter positioned along an imaging axis of said system.

2. The real image projection system of claim 1, further comprising a primary input beam-path or target axis, which represents an imaginary line between a target object and an approximate optical center of a surface of said mirror.

3. The real image projection system of claim 1, wherein said mirror'"'"'s optical axis is tilted at an angle between 10 degrees and 20 degrees in relationship to a target axis of said system, and wherein a front edge of said mirror nearest to a view aperture of said system is lower in relation to a viewing axis of said system than a back edge of said mirror.

4. The real image projection system of claim 1, further comprising:

a) a beamsplitter or partially reflective element located between a target object and said mirror, positioned at an oblique angle of approximately 45 degrees to an optical axis of said mirror, with a top of said beamsplitter nearest to said mirror being positioned at a greater distance from a view aperture of said system than a bottom edge of said beamsplitter, which is located nearest said target object; and

b) a partially reflective coating or surface on a front surface of said beamsplitter, or a side of said beamsplitter facing said mirror and viewing aperture, wherein a target axis or beam-path from said target object to said mirror transmits through said beamsplitter at a brightness level relative to the transmission of said beamsplitter.

5. The real image projection system of claim 1, further comprising:

a) a target axis, or a diverging imaging beam-path from a target object, that passes through a beamsplitter and strikes said mirror at an angle non-coincident with said optical axis of said mirror at an angle between 10 and 20 degrees; and

b) a reflected convergent beam-path, or imaging axis, being reflected off of a surface of said mirror at a complementary angle to said target axis, relative to said optical axis of said mirror, wherein said imaging axis reflects at an angle, in a direction away from a viewing aperture of said system, equal to twice said tilted angle of said mirror in relation to said target axis.

6. The real image projection system of claim 1, comprising an imaging axis or converging beam-path that strikes a beamsplitter reflective surface and reflects at a complementary angle off of said beamsplitter, toward a viewing aperture of said system, wherein a portion of said imaging axis is 90 degrees to a target axis, assuming said beamsplitter is positioned at 45 degrees to said optical axis of said mirror, and is parallel to said viewing axis of said system.

7. The real image projection system of claim 1, comprising a real image positioned along a viewing axis of said system at a focal point of said system, or at a distance equal to twice a focal length of said mirror, if said mirror is a parabola, or at a distance equal to a radius of a curved sphere, assuming a 1×

magnification, wherein a target object is located at a distance from said mirror equal to a radius of said mirror.

8. The real image projection system of claim 7, wherein a position of said target object is other than at a center point of radius for creating a magnified or de-magnified real image.

9. The real image projection system of claim 1, further comprising a background object or monitor or projection screen that is viewed through a beamsplitter, located behind a real image, along a viewing axis of said system.

10. The real image projection system of claim 9, wherein said background object is anything that emits, transmits or reflects light.

11. The real image projection system of claim 1, comprising an aspheric surface of revolution on a concave surface of said mirror.

12. The real image projection system of claim 11, further comprising a reflective coating on said concave surface of revolution.

13. The real image projection system of claim 1, wherein one of said two different surfaces of revolution is on a concave surface of said mirror, and another of said two different surfaces of revolution is on a convex surface of said mirror.

14. The real image projection system of claim 13, comprising an aspheric surface of revolution on said concave surface, and a standard conic or asphere surface of revolution on said convex surface, wherein said convex surface is optically coated with a reflective surface.

15. The real image projection system of claim 13, comprising a standard conic or aspheric surface of revolution on said concave surface, and an aspheric surface of revolution on said convex surface, wherein said convex surface is optically coated with a reflective surface.

16. The real image projection system of claim 13, further comprising an anti-reflective coating on said concave surface of revolution to reduce secondary ghost reflections.

17. The real image projection system of claim 1, wherein one of said two different surfaces of revolution is an aspheric surface of revolution on a concave surface of said mirror, and another of said two different surfaces of revolution is on a convex surface of said mirror, and wherein said optical axis of said mirror is positioned at an angle between 10 and 20 degrees, relative to said axis of said system.

18. The real image projection system of claim 1, wherein said mirror comprises precision surfaces of revolution, wherein one of said two different surfaces of revolution is a standard conic or aspheric surface of revolution on a concave surface of said mirror, and another of said two different surfaces of revolution is an aspheric surface of revolution on a convex surface of said mirror, wherein said convex surface is optically coated with a reflective surface, and wherein said mirror is formed by an injection molding process, using a precision mold.

19. A precision injection mold for forming the mirror of claim 18, comprising:

a) mold inserts having highly precise surfaces of revolution, formed through a single-point diamond-turning process; and

b) precision polishing, performed with a multiple floating spindle polishing head.

20. The mirror of claim 18, comprising mounting tabs attached to edges of said mirror, centered on four sides of said mirror, wherein said mirror is held within a display in an unstressed manner, with single point contact on both top and bottom mounting tabs.

21. The real image projection system of claim 1, comprising a neutral density filter in the beam-path, for ghost image reduction.

22. The real image projection system of claim 21, wherein said neutral density filter comprises a neutral density material, or a neutral density coating, wherein light transmitting through said filter is partially absorbed in near equal amounts across the visible light spectrum.

23. The real image projection system of claim 21, wherein said neutral density filter comprises a beamsplitter of neutral density material, or having a neutral density coating, wherein light transmitting through said beamsplitter is partially absorbed in near equal amounts across the visible light spectrum.

24. The real image projection system of claim 21, wherein said neutral density filter comprises a neutral density substrate or neutral density coating on a surface opposite a reflective coating, and a configuration whereby said mirror, a beamsplitter and a real image are located on a common optical axis, and at approximately 90 degrees to a portion of a target axis extending from a target object to said beamsplitter.

25. The real image projection system of claim 1, comprising a distorted input screen image with pin-cushioning effect, wherein said screen image is distorted in a configuration whereby distortion caused by field curvature distortion is counteracted, thereby causing a video image to distort in a manner opposite of fish-eye effect, thereby producing a true scaled, undistorted real image of an object represented.