Image pickup system with auto focus mode

1. An image pickup system comprising:

an image pickup apparatus in which, photoelectric conversion cells which convert an optical image which has been formed by a taking lens to an electric signal, are arranged two-dimensionally, wherein

at least some of the photoelectric conversion cells are arranged to output a signal for detecting an amount of defocus, and

the photoelectric conversion cells which output the signal for detecting the amount of defocus constitute at least two photoelectric conversion cell groups, each receiving a light beam from a pupil area having a different area, and

each photoelectric conversion cell group has a plurality of photoelectric conversion cell columns, and

the image pickup system further comprising:

a calculating section which has an auto focus (AF) mode which generates a defocus signal by comparing mutually the signals for detecting the amount of defocus, which have been output from the two photoelectric conversion cell groups; and

a correction section which corrects the signal for detecting the amount of defocus, from information related to distortion of the taking lens,

wherein the taking lens satisfies the following conditional expression:

0.05≦|(1 −Yim /( f ·tan(ω im )))|≦0.35

where f denotes a focal length of the taking lens,

Yim denotes an arbitrary image height in a range of 0.4 to 0.8 when a distance from a center in an effective image pickup surface of an electronic image pickup element up to the farthest point is let to be 1, and

ωim denotes an angle with respect to an optical axis in an object-point direction corresponding to image points connecting from the center on the effective image pickup surface of the electronic image pickup element up to a position of Yim.

2. The image pickup system according to claim 1 , wherein the correction section corrects signal information of one photoelectric conversion cell column of the photoelectric conversion cell group, and let the signal information which has been corrected, to be one set of signal information, and corrects signal information of the photoelectric conversion cell column of another photoelectric conversion cell group, and let the signal information which has been corrected, to be another set of signal information, and calculates phase-difference information from these two sets of signal information.

3. The image pickup system according to claim 1 , wherein the correction section corrects a signal for detecting a defocus signal by information for correcting distortion of a recorded image of the taking lens stored in a lens-information recording section.

4. The image pickup system according to claim 1 , wherein a correction amount of a signal for detecting the defocus signal and a correction value of image data which is recorded have different modes.

5. The image pickup system according to claim 1 , wherein

the taking lens is detachably attachable, and

when information related to distortion of an image of the taking lens cannot be read in a predetermined format by the taking lens which has been installed, the correction of distortion is not to be carried out.

6. The image pickup system according to claim 1 , wherein the correction of signal for detecting the defocus signal is to be carried out at a position where image height is more than 0.5.