Image-forming optical apparatus having a decentered optical surface

• US 5,936,773 A
• Filed: 04/30/1998
• Issued: 08/10/1999
• Est. Priority Date: 07/02/1997
• Status: Expired due to Term

• Current Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Original Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Inventors: Togino, Takayoshi
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): MACK, RICKY LEVERN
• Application Number:
  US09/069,982
• Time in Patent Office: 467 Days
• Field of Search: 359/630, 359/631, 359/633, 359/637
• US Class Current: 359/630
• CPC Class Codes: G02B 13/22 Telecentric objectives or lens systems
• 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 17/0832 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 17/086 wherein the system is made of a single block of optical material, e.g. solid catadioptric systems
• CPC Class Codes: G02B 23/2407 Optical details
• CPC Class Codes: G02B 27/0025 for optical correction, e.g. distorsion, aberration
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: H04N 23/55 Optical parts specially adapted for electronic image sensors; Mounting thereof
• CPC Class Codes: H04N 23/555 for picking-up images in sites, inaccessible due to their dimensions or hazardous conditions, e.g. endoscopes or borescopes
• CPC Class Codes: H04N 23/63 by using electronic viewfinders
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements

Abstract

A compact image-forming optical apparatus which is free from moire fringes and capable of providing an aberration-free, clear image of minimal distortion even at a wide field angle. The image-forming optical apparatus has an objective optical system (104) and an electronic image pickup device (108). The objective optical system (104) has at least one reflecting surface (106, 107) decentered such that the whole surface is tilted with respect to the axial principal ray. The reflecting surface has a rotationally asymmetric surface configuration that corrects rotationally asymmetric decentration aberrations caused by decentration. A low-pass member (103) is disposed in the vicinity of a pupil plane (101) closer to the object than the reflecting surface. The low-pass member cuts off a high-frequency component concerning the object image in a bundle of rays led to the electronic image pickup device (108).

Claims

1. In an image-forming optical apparatus comprising an objective optical system and an electronic image pickup device which is disposed in a plane where an image of an object is formed by said objective optical system,

the improvement wherein said objective optical system has at least one reflecting surface decentered such that a whole of said surface is tilted with respect to an axial principal ray defined by a light ray emanating from a center of the object and passing through a center of a pupil to reach a center of the object image,

said reflecting surface having a rotationally asymmetric surface configuration that corrects rotationally asymmetric decentration aberrations caused by decentration, and

wherein a low-pass member is disposed in a vicinity of a pupil plane closer to the object than said reflecting surface, said low-pass member cutting off a high-frequency component concerning the object image in a bundle of light rays led to said electronic image pickup device.

2. An image-forming optical apparatus according to claim 1, wherein said objective optical system has a prism member formed from a medium having a refractive index (n) larger than 1 (n>

1), and

wherein said prism member has at least three optical surfaces including;

a first surface disposed closest to the object and having an action through which a bundle of light rays enters said prism member;

a third surface which is a reflecting surface having said rotationally asymmetric surface configuration to reflect the ray bundle entering said prism member; and

a second surface having an action through which the ray bundle exits from said prism member.

3. An image-forming optical apparatus according to claim 2, wherein said prism member is formed such that a bundle of light rays from the object enters said prism member through said first surface and is first reflected by said second surface and then reflected by said third surface so as to exit from said prism member through said second surface.

4. An image-forming optical apparatus according to claim 2, wherein said second surface is arranged to reflect the light rays entering through said first surface by total reflection, so that said second surface has both reflecting and transmitting actions.

5. An image-forming optical apparatus according to claim 2, wherein said second surface is a semitransparent reflecting surface provided with a half-mirror coating.

6. An image-forming optical apparatus according to claim 2, wherein said third surface is a reflecting mirror surface provided with a mirror coating.

7. An image-forming optical apparatus according to claim 2, wherein said low-pass member is formed on said first surface of said prism member.

8. An image-forming optical apparatus according to claim 2, wherein said low-pass member is an optical element disposed on an object side of said first surface of said prism member at a distance from said first surface.

9. An image-forming optical apparatus according to claim 7 or 8, wherein at least one surface of said low-pass member has a polyhedral configuration having a spatial frequency low-pass filter function, wherein at least two of lines normal to a plurality of surfaces of said polyhedral configuration at approximately respective centers are in a skew relation with respect to an optical axis, and a boundary line between said plurality of surfaces is decentered with respect to the optical axis of said optical system.

10. An image-forming optical apparatus according to claim 7 or 8, wherein at least one surface of said low-pass member has a polyhedral configuration having a spatial frequency low-pass filter function, wherein at least two of lines normal to a plurality of surfaces of said polyhedral configuration at approximately respective centers are in a skew relation with respect to an optical axis, and a boundary line between said plurality of surfaces and its vicinities are covered with a substance which does not transmit light.

11. An image-forming optical apparatus according to claim 7 or 8, wherein at least one surface of said low-pass member has a polyhedral configuration having a spatial frequency low-pass filter function, wherein at least two of lines normal to a plurality of surfaces of said polyhedral configuration at approximately respective centers are in a skew relation with respect to an optical axis, and an area of a defective surface configuration portion in a vicinity of a boundary line between said plurality of surfaces satisfies the condition (15).

12. An image-forming optical apparatus according to claim 7 or 8, wherein said low-pass member is disposed at a position where the condition (21) is satisfied.

13. An image-forming optical apparatus according to claim 7 or 8, which satisfies the condition (12) and, at the same time, one of the conditions (22) and (23).

14. An image-forming optical apparatus according to claim 8, wherein said low-pass member is an optical element having an ordinary lens surface on one side thereof, said optical element having on the other side thereof at least two slant surfaces split with respect to an optical axis which are in a skew relation to each other.

15. An image-forming optical apparatus according to claim 9, wherein at least one of said plurality of surfaces is one of a spherical surface and an aspherical surface.

16. An electronic camera having the image-forming optical apparatus according to any one of claims 1 to 8 and 14, wherein said image-forming optical apparatus is used as an image pickup system.

17. A video endoscope having the image-forming optical apparatus according to any one of claims 1 to 8 and 14, wherein said image-forming optical apparatus is used as an image pickup system.