Projection optical system, magnification projection optical system, magnification projection apparatus, and image projection apparatus

• US 7,637,618 B2
• Filed: 09/19/2008
• Issued: 12/29/2009
• Est. Priority Date: 02/06/2003
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Takaura, Atsushi, Fujita, Kazuhiro, Sakuma, Nobuo
• Primary Examiner(s): Koval; Melissa J
• Application Number:
  US12/233,672
• Publication Number:
  US 20090015910A1
• Time in Patent Office: 466 Days
• Field of Search: 353/30, 353/31, 353/34, 353/37, 353/69, 353/70, 353 77- 79, 353/99, 353/102, 359/449, 359/649, 359/650, 359656-661, 359/663, 359/668, 359726-731, 359/739, 359/364, 359/365
• US Class Current: 353/37
• 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 17/0816 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 17/0848 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 17/0852 having a field corrector only
• 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 projection apparatus illuminating an image display panel forming an image in accordance with a modulating signal with illumination light from a light source. The projection optical system includes first and second optical systems arranged along an optical path defining an upstream-downstream direction in the order described from upstream to downstream on the downstream side of the image display panel. The first optical system includes at least one dioptric system and has positive power. The second optical system includes at least one reflecting surface having power and has positive power. The image formed by the image display panel is formed as an intermediate image in the optical path, and the intermediate image is magnified and projected.

Claims

1. A projection optical system, comprising:

a first optical system including at least one dioptric system and having positive power; and

a second optical system including one or more reflecting surfaces having power, the second optical system having positive power as a whole,

wherein the first and second optical systems are arranged along an optical path defining an upstream-downstream direction in an order described from upstream to downstream on a downstream side of an object surface;

an object image is temporarily formed as an intermediate image, and thereafter, is formed as a final image; and

with respect to an optical axis of an optical element positioned at a furthest upstream end of the first optical system and having refractive power, at least one of other optical elements is shifted or tilted.

2. The projection optical system as claimed in claim 1, wherein the reflecting surfaces of the second optical system includes at least one free-form surface.

3. The projection optical system as claimed in claim 2, wherein only one of the reflecting surfaces of the second optical system, which one is positioned furthest on a side of a position where the final image is formed, is the free-form surface.

4. The projection optical system as claimed in claim 1, wherein one of the reflecting surfaces of the second optical system, which one has positive power and from which one a light beam made incident on the second optical system is reflected first, is rotationally symmetric.

5. The projection optical system as claimed in claim 4, wherein the one of the reflecting surfaces which one is rotationally symmetric is a spherical reflecting surface.

6. The projection optical system as claimed in claim 1, wherein the first optical system includes only the dioptric system.

7. The projection optical system as claimed in claim 6, wherein the dioptric system of the first optical system excludes an aspheric surface figure.