Focus detecting apparatus having increased SNR by selectively varying or holding constant the number of signals from sensor arrays

摘要

An apparatus for detecting the focus state of an optical system has optical apparatus for forming first and second light distributions of an object. The relative positional relationship of the light distributions varies in accordance with the focus state of the optical system. A light receiving device has first and second ranges, each having a plurality of picture elements. The first and second ranges respectively receive the first and second light distributions. Operation circuitry manipulates the output signals from the first and second ranges by relatively mathematically moving them to calculate a value representing the focus state of the optical system. The operation circuitry selectively executes a first operation in which the number of signals corresponding to each other is varied, and a second operation in which the number of signals corresponding to each other is kept constant.