VARIABLE MAGNIFICATION OPTICAL SYSTEM AND PROJECTOR

• US 20100053737A1
• Filed: 08/24/2009
• Published: 03/04/2010
• Est. Priority Date: 09/02/2008
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: FUJITA, Kazuhiro, Abe, Issei
• Granted Patent: US 8,254,039 B2
• Time in Patent Office: Days
• US Class Current: 359/364
• CPC Class Codes: G02B 17/08 Catadioptric systems used in non-imaging applications G02B19/00
• CPC Class Codes: G02B 17/0852 having a field corrector only
• CPC Class Codes: G02B 17/0896 with variable magnification or multiple imaging planes, including multispectral systems systems with only refractive elements G02B15/14
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066

Abstract

A variable magnification optical system projects an image onto a screen with a sufficient magnification without requiring a large-sized mirror. The variable magnification optical system includes a first optical system through which a light beam modulated with an image signal corresponding to the image is passed; a second optical system disposed downstream of the first optical system in a direction of travel of the light beam along an optical axis; and a reflective optical element having a magnification power that is configured to reflect the light beam from the second optical system toward the screen. A magnification of the image projected on the screen is changed by moving the reflective optical element relative to the object plane, thus changing a distance between the screen and the reflective optical element, while an incident angle of the light beam on the screen is maintained substantially constant.

Claims

1. A variable magnification optical system comprising:

a reflective optical element having a positive magnification power and configured to be movable relative to an object plane; and

a refractive optical system configured to form an intermediate image between the object plane and the reflective optical element, the refractive optical system including plural refractive optical elements,

wherein a substantially constant magnification of the intermediate image is maintained before and after a magnification change by a movement of the reflective optical element by moving at least one of the plural refractive optical elements.

2. The variable magnification optical system according to claim 1, wherein a substantially constant relative position of the intermediate image to the reflective optical element is maintained by moving at least one of the plural refractive optical elements.

3. The variable magnification optical system according to claim 1, wherein, when the reflective optical element is moved, an incident angle of the light beam reflected by the reflective optical element on a projected plane is maintained substantially constant.

4. The variable magnification optical system according to claim 1, wherein, when the reflective optical element is moved, a difference between a maximum angle and a minimum angle of a light beam that passes through the refractive optical system, forming projecting light, with respect to an arbitrary plane is maintained at a substantially constant value.

5. The variable magnification optical system according to claim 1, wherein, when the reflective optical element is moved, an incident angle of a light beam reflected by the reflective optical element that is incident on a projected plane at a maximum angle changes by 5°

or less.

6. The variable magnification optical system according to claim 1, wherein, when the reflective optical element is moved, an incident angle of a light beam reflected by the reflective optical element that is incident on a projected plane at a minimum angle changes by 5°

or less.

7. The variable magnification optical system according to claim 1, wherein, when the reflective optical element is moved, a difference between a maximum angle and a minimum angle of a light beam that passes through the refractive optical system, forming projecting light, with respect to an arbitrary plane varies by 3°

or less.

8. A variable magnification optical system for projecting an image onto a screen, the system comprising:

a first optical system through which a light beam irradiated from an object plane is passed;

a second optical system disposed downstream of the first optical system in a direction of travel of the light beam along an optical axis; and

a reflective optical element having a magnification power that is configured to reflect the light beam from the second optical system toward the screen,

wherein a magnification of the image projected on the screen is changed by moving the reflective optical element relative to the object plane, thus changing a distance between the screen and the reflective optical element, while an incident angle of the light beam on the screen is maintained substantially constant.

9. The variable magnification optical system according to claim 8, wherein at least one of the first optical system and the second optical system includes plural refractive optical elements, and

wherein one or more of the refractive optical elements is moved along the optical axis for focusing the image, depending on an amount of movement of the reflective optical element.

10. The variable magnification optical system according to claim 8, further comprising a lens tube member configured to retain the second optical system and the reflective optical element,

wherein the lens tube member is moved along the optical axis in order to change the distance between the screen and the reflective optical element.