Projection optical system and image projecting apparatus

• US 8,025,415 B2
• Filed: 09/13/2007
• Issued: 09/27/2011
• Est. Priority Date: 09/15/2006
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Takaura, Atsushi, Fujita, Kazuhiro, Abe, Issei
• Primary Examiner(s): Ko; Tony
• Application Number:
  US11/854,920
• Publication Number:
  US 20080068564A1
• Time in Patent Office: 1,475 Days
• Field of Search: 353/98, 353/99, 353/70, 353/77, 353/102, 359/49, 359/680, 359/691, 359/725, 359749-753
• US Class Current: 353/70
• 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 17/0812 off-axis or unobscured systems in which all of the mirrors share a common axis of rotational symmetry
• CPC Class Codes: G02B 17/0852 having a field corrector only
• CPC Class Codes: G03B 21/147 Optical correction of image distortions, e.g. keystone
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066
• CPC Class Codes: H04N 9/3102 using two-dimensional electronic spatial light modulators micromechanical modulators as such G02B26/0833; liquid crystal modulators as such G02F1/13

Abstract

A projection optical system including a first optical system configured to form a second image conjugate to a first image and a second optical system configured to include a reflective optical element which reflects light from the second image and to project a third image conjugate to the second image onto a projection surface is provided, wherein the first optical system includes a stop and at least one optical element with a positive refractive power and at least one optical element with a negative refractive power which are provided between the stop and the second image, and an optical element with a strongest positive refractive power in the at least one optical element with a positive refractive power is provided between the stop and an optical element with a strongest negative refractive power in the at least one optical element with a negative refractive power.

Claims

1. A projection optical system in which plural light beams emitted from an image forming element displaying image information on a conjugate plane A are allowed to be obliquely incident on a conjugate plane B so as to form an enlarged image of an image formed by the image forming element on the conjugate plane B, wherein

the projection optical system comprises, at least,

a first optical system,

a second optical system,

an intermediate image of the image forming element between the first optical system and the second optical system on which the plural light beams are generally converged,

an optical system having a refractive power in the first optical system being composed of only a lens system transmitting the light beams,

the intermediate image being formed by only a refractive power of the first optical system,

the second optical system being a reflective optical system comprising a reflection mirror having a positive refractive power which reflects the light beams and is directly behind the intermediate image,

the first optical system is divided into a first lens group, a second lens group, and a third lens group by a stop and the third lens group includes a maximum lens distance space at the side of the conjugate plane B from the stop, and

the first lens group, the second lens group, and the third lens group have respective positive, positive, and negative refractive powers in sequence from the side of conjugate plane A.

2. The projection optical system as claimed in claim 1, wherein a curved surface of the mirror having a positive refractive power in the second optical system has a shape such that a curvature thereof becomes smaller from its intersection point with an optical axis of the first optical system to a perimeter thereof.

3. The projection optical system as claimed in claim 1, wherein the mirror having a positive refractive power in the second optical system has an anamorphic and polynomial free-form surface having different powers between a minor axis direction and major axis direction of the image forming element.

4. The projection optical system as claimed in claim 1, wherein the mirror having a positive refractive power in the second optical system has a surface with a rotationally symmetric and aspherical shape.

5. The projection optical system as claimed in claim 1, wherein a lens of the first optical system has at least one surface with an aspherical shape.

6. The projection optical system as claimed in claim 5, wherein the aspherical surface in the first optical system is positioned in a third group.

7. The projection optical system as claimed in claim 6, wherein at least one aspherical surface in the third group of the first optical system is positioned on a lens having a positive refractive power.

8. The projection optical system as claimed in claim 1, wherein the intermediate image is curved and tilted with respect to a surface perpendicular to an optical axis of the first optical system.

9. The projection optical system as claimed in claim 1, wherein the projection optical system is generally telecentric from the image forming element to a first surface of the transmittable refractive optical system.

10. The projection optical system as claimed in claim 1, wherein a reflection mirror is arranged between lenses of the first optical system.

11. An image projecting apparatus comprising:

an image forming element displaying image information on a conjugate plane A;

an illuminating optical system illuminating the image forming element; and

a projection optical system allowing plural light beams emitted from the image forming element to be obliquely incident on a conjugate plane B so as to form an enlarged image of an image formed by the image forming element on the conjugate plane B,

wherein the projection optical system includes, at least,

a first optical system,

a second optical system,

an intermediate image of the image forming element between the first optical system and the second optical system on which the plural light beams are generally converged,

an optical system having a refractive power in the first optical system being composed of only a lens system transmitting the light beams,

the intermediate image being formed by only a refractive power of the first optical system,

the second optical system being a reflective optical system comprising a reflection mirror having a positive refractive power which reflects the light beams and is directly behind the intermediate image, and

the first optical system is divided into a first lens group, a second lens group, and a third lens group by a stop and the third lens group includes a maximum lens distance space at the side of the conjugate plane B from the stop, and

the first lens group, the second lens group, and the third lens group have respective positive, positive, and negative refractive powers in sequence from the side of conjugate plane A.