Projection optical system and image display apparatus

• US 8,950,874 B2
• Filed: 09/12/2012
• Issued: 02/10/2015
• Est. Priority Date: 09/16/2011
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Tatsuno, Hibiki
• Primary Examiner(s): CHOWDHURY, SULTAN U.
• Application Number:
  US13/611,578
• Publication Number:
  US 20130070217A1
• Time in Patent Office: 881 Days
• Field of Search: 353/30, 353/34, 353/37, 353/38, 353/94, 353/99, 353/101, 348743-747, 348/798, 348/E5.139, 348/E5.142, 348/E5.143, 359/736, 359/455, 359/627, 359/457, 359/460, 359/471, 359/479, 359/634, 359/640, 349/5, 349 7- 9
• US Class Current: 353/99
• CPC Class Codes: G02B 13/16 for use in conjunction with image converters or intensifiers , or for use with projectors, e.g. objectives for projection TV
• CPC Class Codes: G02B 17/08 Catadioptric systems used in non-imaging applications G02B19/00
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 27/0006 with means to keep optical surfaces clean, e.g. by preventing or removing dirt, stains, contamination, condensation G02B1/18 takes precedence; cleaning in general B08B
• CPC Class Codes: G03B 21/2066 Reflectors in illumination beam in projection beam G03B21/28
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066

Abstract

A projection optical system for use in an image display apparatus having an illumination optical system applying light from a light source, and an image display device receiving the light from the illumination optical system to form a projection image includes a projector lens composed of plural lenses, a first mirror, and a second mirror formed of a concave mirror. The projection optical system is configured to project the projection image onto a projection surface. A projection luminous flux passing through the projector lens to be incident on the first mirror is a luminous flux exhibiting divergence. The projection luminous flux reflected off the second mirror after having reflected off the first mirror is converged once, and the once converged projection luminous flux is projected onto the projection surface. A lens surface of a lens located closest to the first mirror among the lenses of the projector lens is convex.

Claims

1. A projection optical system for use in an image display apparatus having an illumination optical system configured to apply light emitted from a light source, and an image display device configured to receive the light applied from the illumination optical system to form a projection image, the projection optical system comprising:

a projector lens composed of a plurality of lenses;

a first mirror; and

a second mirror formed of a concave mirror, the projection optical system being configured to project the projection image formed by the image display device onto a projection surface, wherein a projection luminous flux passing through the projector lens to be incident on the first mirror is a luminous flux exhibiting divergence, wherein the projection luminous flux reflected off the second mirror after having reflected off the first mirror is converged once, and the once converged projection luminous flux is then projected onto the projection surface, and wherein a lens surface of a lens located closest to the first mirror among the lenses of the projector lens is convex;

wherein a position at which the projection luminous flux reflected off the second mirror is converged is closer to the first mirror than to the second mirror.

2. The projection optical system as claimed in claim 1, wherein

a position at which the projection luminous flux reflected off the second mirror is converged is close to the first mirror.

3. The projection optical system as claimed in claim 1, wherein

the first mirror is a plane mirror.

4. The projection optical system as claimed in claim 1, wherein

a position at which the projection luminous flux reflected off the second mirror is converged is close to a virtual reflection plane extended from a reflection plane of the first mirror.

5. The image display apparatus comprising:

the projection optical system as claimed in claim 1;

the illumination optical system configured to apply the light emitted from the light source; and

the image display device configured to receive the light applied from the illumination optical system to form the projection image.

6. The image display apparatus as claimed in claim 5, wherein

each of angles formed between rays of light incident on an image projected onto the projection surface at a center in a horizontal direction and a normal line of the projection surface has a same sign.

7. The image display apparatus as claimed in claim 5, further comprising:

a dustproof member between the second mirror and the projection surface, wherein

a position at which the projection luminous flux reflected off the second mirror is converged is close to the dustproof member.

8. The image display apparatus as claimed in claim 5, wherein

an end of the projector lens located closest to the first mirror among the lenses of the projector lens is protruded more toward a first mirror side than a side end of a lens barrel holding the projector lens.

9. The image display apparatus as claimed in claim 5, wherein

the lens located closest to the first mirror among the lenses of the projector lens is an atypical lens partially having a cutout part.

10. The image display apparatus as claimed in claim 5, wherein

the image display device is a reflection image display device that includes a plurality of two-dimensionally arranged micromirrors, and wherein emission of reflected light is switched on or off by changing an angle of each of the micromirrors to be in an ON state or an OFF state.

11. A projection optical system for use in an image display apparatus having an illumination optical system configured to apply light emitted from a light source, and an image display device configured to receive the light applied from the illumination optical system to form a projection image, the projection optical system comprising:

a lens optical system composed of a plurality of lens groups; and

a mirror optical system composed of a first mirror, and a second mirror formed of a concave mirror, a projection luminous flux passing through the lens optical system is incident on the first mirror, and the projection optical system being configured to project the projection image formed by the image display device onto a projection surface, wherein an intermediate image is formed between the first mirror and the second mirror, the intermediate image being composed of pixels associated with the image display device located closest to an optical axis of the lens optical system, and wherein a lens surface of a lens group located closest to the first mirror among the lens groups of the lens optical system is convex;

wherein a position at which the projection luminous flux reflected off the second mirror is converged is closer to the first mirror than to the second mirror.

12. The projection optical system as claimed in claim 11, wherein

a lens group located closest to the image display device among the lens groups of the lens optical system includes an aperture diaphragm.

13. The projection optical system as claimed in claim 12, wherein

a total refracting power from a lens group next to the lens group having the aperture diaphragm to the lens group located closest to the first mirror among the lens groups of the lens optical system is a negative refractive power.

14. The image display apparatus as claimed in claim 12, further comprising:

an aspherical lens located close to the aperture diaphragm.

15. The image display apparatus comprising:

the projection optical system as claimed in claim 11;

the illumination optical system configured to apply the light emitted from the light source; and

the image display device configured to receive the light applied from the illumination optical system to form the projection image.

16. The image display apparatus as claimed in claim 15, further comprising:

a dustproof member between the second mirror and the projection surface, wherein

the dustproof glass is approximately parallel to a plane of the image display device.

17. The image display apparatus as claimed in claim 15, wherein

an intermediate image is formed between the first mirror and the second mirror, the intermediate image being composed of pixels associated with the image display device located farthest from an optical axis of the lens optical system.

18. The image display apparatus as claimed in claim 15, wherein

the second mirror is a free-form surface mirror.

19. The image display apparatus as claimed in claim 15, wherein

the image display device is a reflection image display device that includes a plurality of two-dimensionally arranged micromirrors, and wherein emission of reflected light is switched on or off by changing an angle of each of the micromirrors to be in an ON state or an OFF state.