Patent ID: 8508650

Claim:
An image pickup system comprising: an image pickup apparatus; and a mount adaptor operable to adjust a flange focal length between the image pickup apparatus and an interchangeable lens, wherein the mount adaptor comprises: a phase-difference focus detection unit operable to output a first phase-difference focus detection signal, wherein the first phase-difference focus detection signal corresponds to a plurality of distance-measurement points of the phase-difference focus detection unit, and an optical device operable to separate a first incident light into a second incident light and a third incident light, wherein the first incident light is transmitted from the interchangeable lens, wherein the second incident light enters the image pickup apparatus, wherein the third incident light enters the phase-difference focus detection unit, and wherein the image pickup apparatus comprises: an image pickup device operable to output a second phase-difference focus detection signal, wherein the second phase-difference focus detection signal corresponds to a plurality of distance-measurement points of the image pickup device and wherein the plurality of distance-measurement points of the phase-difference focus detection unit are less in number than the plurality of distance-measurement points of the image pickup device, and a controller operable to select either of the first phase-difference focus detection signal and the second phase-difference focus detection signal based on the satisfaction of a predetermined condition and operable to perform focusing.