Autofocus adapter

• US 20030160888A1
• Filed: 02/05/2003
• Published: 08/28/2003
• Est. Priority Date: 02/26/2002
• Status: Active Grant

• Current Assignee: Fujinon Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fujinon Corporation (Fujifilm Holdings Corporation)
• Inventors: Yoshikawa, Kazuo
• Granted Patent: US 7,233,358 B2
• Time in Patent Office: Days
• US Class Current: 348/357
• CPC Class Codes: H04N 23/55 Optical parts specially adapted for electronic image sensors; Mounting thereof
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method

Abstract

An autofocus adapter for detachably mounting between an imaging lens and a camera body and for detecting the focus state of the imaging lens is disclosed. The autofocus adapter includes two focus state detecting elements with light receiving surfaces slightly displaced in front and in back of a desired position of focus of the imaging lens. A beamsplitter directs some light to the two focus state detecting elements and some light through the autofocus adapter for forming an image in a camera. The autofocus adapter includes a relay lens system and electronics for detecting the focus state and controlling the focus of the imaging lens to an in-focus state based on the images detected at the two focus state detecting elements. The beamsplitter may deflect equal amounts of light to the two light receiving surfaces, and the autofocus adapter may include an iris.

Claims

1. An autofocus adapter for detachably mounting between an imaging lens and a camera body and for detecting the focus state of the imaging lens, the autofocus adapter including an object side and an image side and comprising:

two focus state detecting elements, each focus state detecting element including a light receiving surface;

light dividing means for dividing light that enters the object side of the autofocus adapter in order to direct some of the light toward the light receiving surfaces of the two focus state detecting elements and to direct some of the light toward the rear of the autofocus adapter;

a relay lens system that receives the light that the light dividing means directs toward the rear of the autofocus adapter, wherein the relay lens system defines an optical axis of the autofocus adapter and the light dividing means deflects light toward each said light receiving surface along a separate optical axis;

focus state detection means for detecting, when an imaging lens is attached to the autofocus adapter, the focus state of an imaging lens based on images received at the light receiving surfaces of said two focus state detecting elements; and

control means for controlling, when the autofocus adapter is detachably mounted to an imaging lens, the focus of the imaging lens based on the focus state detected by the focus state detection means.

2. The autofocus adapter of claim 1, and further comprising:

an iris that receives light that is directed toward the rear of the autofocus adapter from the light dividing means.

3. The autofocus adapter of claim 1, wherein the optical path length along one said separate optical axis to one said light receiving surface is substantially shorter than the optical path length along the other said separate optical axis to the other said light receiving surface.

4. The autofocus adapter of claim 2, wherein the optical path length along one said separate optical axis to one said light receiving surface is substantially shorter than the optical path length along the other said separate optical axis to the other said light receiving surface.

5. The autofocus adapter of claim 1, wherein the light dividing means directs substantially the same amount of light toward each said light receiving surface.

6. The autofocus adapter of claim 2, wherein the light dividing means directs substantially the same amount of light toward each said light receiving surface.

7. The autofocus adapter of claim 3, wherein the light dividing means directs substantially the same amount of light toward each said light receiving surface.

8. The autofocus adapter of claim 4, wherein the light dividing means directs substantially the same amount of light toward each said light receiving surface.

9. The autofocus adapter of claim 3, wherein a position along said first optical axis exists where a real image defined so that a wavefront of a light beam entering the front end of the autofocus adapter and forming that real image would be converted by the relay lens system into a wavefront at the rear end of the autofocus adapter that is capable of forming a real unity magnification image of that real image without any additional focusing optics, and an optical path length to said position along said first optical axis is halfway between said optical path length along one said separate optical axis to one said light receiving surface and said optical path length along the other said separate optical axis to the other said light receiving surface.

10. The autofocus adapter of claim 9, wherein the light dividing means directs substantially the same amount of light toward each said light receiving surface.

11. The autofocus adapter of claim 4, wherein a position along said first optical axis exists where a real image defined so that a wavefront of a light beam entering the front end of the autofocus adapter and forming that real image would be converted by the relay lens system into a wavefront at the rear end of the autofocus adapter that is capable of forming a real unity magnification image of that real image without any additional focusing optics, and an optical path length to said position along said first optical axis is halfway between said optical path length along one said separate optical axis to one said light receiving surface and said optical path length along the other said separate optical axis to the other said light receiving surface.

12. The autofocus adapter of claim 11, wherein the light dividing means directs substantially the same amount of light toward each said light receiving surface.