Imaging optical system and endoscope provided with imaging optical system

• US 7,576,310 B2
• Filed: 11/16/2007
• Issued: 08/18/2009
• Est. Priority Date: 04/27/2005
• Status: Active Grant

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Medical Systems Corporation (Olympus Corporation)
• Inventors: Orihara, Tatsuya, Konno, Mitsujiro
• Primary Examiner(s): Epps; Georgia Y
• Assistant Examiner(s): BUI PHO, PASCAL M
• Application Number:
  US11/941,502
• Publication Number:
  US 20080062260A1
• Time in Patent Office: 641 Days
• Field of Search: 250/208.1, 250/216, 359/718, 359/719, 600/160, 600/176, 600/101, 600/103, 600/117, 600/118, 348/45, 348/65, 348/68, 356/241.1
• US Class Current: 250/208.1
• CPC Class Codes: A61B 1/00096 Optical elements
• CPC Class Codes: A61B 1/00188 with focusing or zooming features
• CPC Class Codes: A61B 1/041 Capsule endoscopes for imaging
• CPC Class Codes: G02B 13/06 Panoramic objectives; So-called "sky lenses" including panoramic objectives having reflecting surfaces
• CPC Class Codes: G02B 23/243 Objectives for endoscopes
• CPC Class Codes: H04N 23/54 Mounting of pick-up tubes, electronic image sensors, deviation or focusing coils
• 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

Abstract

An imaging optical system includes a spherical or nearly spherical viewing port, an objective lens that includes an aspheric surface and is formed as a single lens element, and a solid-state image sensor that receives an image formed by the imaging optical system. Specified conditions are satisfied by the imaging optical system and the objective lens so that an in-focus image having low distortion, sufficient contrast, and formed by light rays of restricted angles of incidence is formed even for an object in contact with the viewing port. The specified conditions relate to features of the imaging optical system such as focal length and f-number of the imaging optical system, astigmatism and distortion of the imaging optical system, and pixel pitch of the solid-state image sensor. An endoscope that includes the imaging optical system is also disclosed.

Claims

1. An imaging optical system including an optical axis, the imaging optical system comprising:

a spherical or nearly spherical transparent viewing port;

an objective lens that includes at least one aspheric surface and that optically forms an image of an object along said optical axis, said objective lens being formed as a single lens element having positive refractive power; and

a solid-state image sensor for converting said image into an electronic signal and that has an image-receiving surface for receiving said image, said image-receiving surface being perpendicular to said optical axis and intersecting said optical axis at the center of an effective imaging area of the image-receiving surface;

wherein

at least one of the following conditions is satisfied

Δ

S<

8·

p/(tan(sin<sup>−

1</sup>(1/(2·

Fno))))

Δ

M<

8·

p/(tan(sin<sup>−

1</sup>(1/(2·

Fno))))

where

Δ

S is the distance in the direction of said optical axis between points of a sagittal image surface of said image at distances IH/2 and IH from said optical axis along straight lines perpendicular to said optical axis, and the point at the distance IH is the farthest point from said optical axis within said effective imaging area;

p is the pixel pitch of said solid-state image sensor;

Fno is the effective f- number of the imaging optical system; and

Δ

M is the distance in the direction of said optical axis between points of a meridional image surface of said image at distances IH/2 and IH from said optical axis along straight lines perpendicular to said optical axis, and the point at the distance IH is the farthest point from said optical axis within said effective imaging area.

2. The imaging optical system according to claim 1, wherein the following condition is also satisfied:

w/2>

50°

where

w is the field angle of the imaging optical system for said effective imaging area.

3. An endoscope comprising:

the imaging optical system as set forth in claim 1, said object being viewed through said transparent viewing port; and

a display device for displaying an image produced from the image received by said solid-state image sensor;

wherein

the following condition is satisfied;

Ra>

0.12 mm

where

Ra is the width, in mm, of a white and black line pair having ten per cent contrast when said white and black line pair forms said object and said white and black line pair are imaged on said image-receiving surface at a distance 4·

IH/5 from said optical axis and IH is the distance of the farthest point from said optical axis within said effective imaging area.

4. An endoscope including an optical axis, the endoscope comprising:

the imaging optical system as set forth in claim 1;

said solid-state image sensor includes an image-receiving surface for receiving said image, said image-receiving surface being perpendicular to said optical axis and intersecting said optical axis at the center of an effective imaging area of said image-receiving surface; and

the following conditions are satisfied;

1.51>

D/fL>

0.94

0°

<

|Tw|<

16.5°

where

D is the thickness of said objective lens along its axis of symmetry;

fL is the focal length of the entire imaging optical system; and

Tw is the angle of incidence of a principal ray of said objective lens on said image-receiving surface at the farthest point from said optical axis when said image is formed on said image-receiving surface.

5. The imaging optical system according to claim 1, wherein:

said solid-state image sensor defines an effective imaging area centered on said optical axis; and

the following condition is satisfied

−

20%<

Δ

D<

26%

where

Δ

D is the amount of distortion of said image as determined at portions of said image about points of an image surface of said image at distances IH/2 and IH from said optical axis along straight lines perpendicular to said optical axis, and the point at the distance IH is the farthest point from said optical axis within said effective imaging area.