Projection optical system and image projection device

• US 8,905,550 B2
• Filed: 05/09/2011
• Issued: 12/09/2014
• Est. Priority Date: 05/18/2010
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Takahashi, Tatsuya, Fujita, Kazuhiro, Abe, Issei
• Primary Examiner(s): Dowling, William C
• Application Number:
  US13/643,177
• Publication Number:
  US 20130235356A1
• Time in Patent Office: 1,310 Days
• Field of Search: 353/69, 353/70, 353/74, 353/77, 353/78, 353/79, 353/98, 353/99
• US Class Current: 353/78
• 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: G03B 21/14 Details
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066

Abstract

A disclosed projection optical system projects images on a surface to be projected on. The projection optical system includes a first optical system including at least one refraction optical system and having positive power as a whole, a folding mirror, and a second optical system including at least one reflection surface having power and having positive power as a whole. Further the folding mirror folds a light path from the first optical system to the second optical system, and in a plane including an optical axis of the first optical system and a normal line of the surface to be projected on, the following conditional expressions (1) through (3) are satisfied (1) 0.43≦d₁, (2) 0.43≦d₂, and (3) 0.7≦d₂/d₁≦2.0.

Claims

1. A projection optical system projecting images on a surface to be projected on, the projection optical system comprising:

a first optical system including at least one refraction optical system and having positive power as a whole;

a folding mirror; and

a second optical system including at least one reflection surface having power and having positive power as a whole;

wherein the folding mirror folds a light path from the first optical system to the second optical system, in a plane including an optical axis of the first optical system and a normal line of the surface to be projected on,

wherein, when a projection distance refers to a distance, which is on a line orthogonal to the surface to be projected on, from the surface to be projected on to a position which is inside an area where light is reflected by the second optical system and which is a farthest from the surface to be projected on and a projection size refers to a size in a horizontal direction of an image projected on the surface to be projected on, a ratio of the projection distance to the projection size is less than or equal to 0.23, and

wherein the following conditional expressions (1) through (3) are satisfied

0.43≦

d₁;

 

 

(1)

0.43≦

d₂;

 

 

(2)

and

0.7≦

d₂/d₁≦

2.0, 

 

(3)

further d₁ is expressed in the following equation (1)

2. The projection optical system according to claim 1,

wherein the following conditional expression (4) is satisfied

0.43≦

d₃, 

 

(4)

further d₃ is expressed in the following equation (2)

3. The projection optical system according to claim 1,

wherein the following conditional expression (5) is satisfied

6.3≦

l₂/f≦

9.0, 

 

(5)

where

a symbol l₂ denotes a distance of light from a surface in the first optical system to the second optical system, the light being reflected by the folding minor at a position closest to an outer end which is farther from the first optical system of the outer ends of the folding mirror, the surface being closest to the folding mirror.

4. The projection optical system according to claim 1,

wherein the reflection surface of the second optical system is an adjustable curved surface.

5. The projection optical system according to claim 1,

wherein the refraction optical system includes an aspheric-shaped refracting surface.

6. The projection optical system according to claim 1,

wherein the folding mirror is a flat mirror.

7. The projection optical system according to claim 1,

wherein the first optical system is a coaxial system.

8. The projection optical system according to claim 1,

wherein θ

₂ is within a range 45°

≦

θ

₂≦

60°

.

9. An image projection device,

wherein irradiation light from a light source is irradiated onto an image forming element where images are formed based on modulation signals, and the images formed on the image forming element are enlarged and projected onto a surface to be projected on using the projection optical system according to claim 1.