Taking lens having focus determination optical system

1. A taking lens, comprising:

a picture-taking optical system which allows object light to enter an image-capturing element for picture-taking of a camera, the picture taking optical system including a first optical path and a first relay lens in the first optical path movable along a first optical axis and forming an image of the object light on an image-capturing plane of the image-capturing element;

a light-splitting device in the first optical path on the opposite side of the first relay lens from the image-capturing element splitting a portion of object light to a second optical path different than the first optical path;

a focus determination optical system in the second optical path including a focus status determination image-capturing element and a second relay lens movable along a second optical axis different than the first optical axis and forming an image of the object light on an image-capturing plane of the focus status detecting image-capturing element;

a picture-taking optical length adjusting device which adjusts an optical length of the picture-taking optical system by moving the first relay lens along the first optical path; and

a focus determination optical length adjusting device which adjusts an optical length of the focus detennination optical system by moving the second relay lens along the second optical path,

wherein a plurality of focus status determination image-capturing elements, each having a different optical length, are provided in the focus determination optical length adjusting device.

2. The taking lens as defined claim 1 , further comprising a coupling device which couples the picture-taking optical length adjusting device and the focus determination optical length adjusting device in such a way as to operate interlocked with each other.

3. The taking lens as defined in claim 1 , further comprising an indicating device which indicates a focus status determined by the focus determination optical system.

4. The taking lens as defined claim 3 , further comprising a coupling device which couples the picture-taking optical length adjusting device and the focus determination optical length adjusting device in such a way as to operate interlocked with each other.

5. A taking lens, comprising:

a picture-taking optical system which allows object light to enter an image-capturing element for picture-taking of a camera;

a focus determination optical system which splits the object light and allows the split light to enter a focus status determination image-capturing element, the focus determination optical system including an image capturing plane at a first angle to the split light entering the focus status determination image capturing element;

a picture-taking optical length adjusting device which adjusts an optical length of the picture-taking optical system; and

a focus determination optical length adjusting device which adjusts an optical length of the focus determination optical system by moving the focus status determination image-capturing element relative to the image-capturing element for picture-taking and keeps said image capturing plane at said first angle to the split light entering the focus status determination image capturing element.

6. The taking lens of claim 5 wherein said picture-taking optical length adjusting device is mechanically coupled to said focus determination optical length adjusting device.

7. The taking lens of claim 5 wherein said picture-taking optical length adjusting device is selectively mechanically coupled to said focus determination optical length adjusting device.

8. The taking lens of claim 5 wherein the optical length of said focus determination optical system is changed in response to a change in the optical length of the picture taking optical system.