Autofocus adaptor

1. An autofocus adaptor for detachably mounting between an imaging lens and a camera body and for detecting the focus state of the imaging lens, the autofocus adaptor 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 adaptor 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 adaptor;

a relay lens system that receives the light that the light dividing means directs toward the rear of the autofocus adaptor, wherein the relay lens system defines an optical axis of the autofocus adaptor 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 adaptor, 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 adaptor 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, and further comprising:

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

2. The autofocus adaptor 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.

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

4. The autofocus adaptor of claim 2 , 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 adaptor and forming that real image would be converted by the relay lens system into a wavefront at the rear end of the autofocus adaptor 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.

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

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

7. An autofocus adaptor for detachably mounting between an imaging lens and a camera body and for detecting the focus state of the imaging lens, the autofocus adaptor 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 adaptor 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 adaptor;

a relay lens system that receives the light that the light dividing means directs toward the rear of the autofocus adaptor, wherein the relay lens system defines an optical axis of the autofocus adaptor 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 adaptor, 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 adaptor 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;

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; and

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 adaptor and forming that real image would be converted by the relay lens system into a wavefront at the rear end of the autofocus adaptor 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.

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