Patent ID: 8482656

Claim:
An apparatus for detecting an in-focus state, comprising: a plurality of line sensors arranged on a projection area of an optical image-forming system; a plurality of monitor sensors arranged on the projection area, each monitor sensor being adjacent to a corresponding line sensor and monitoring a quantity of light incident on a corresponding line sensor; an electric charge accumulation controller that controls the timing of the completion of an accumulation of electric charges in said plurality of line sensors on the basis of a monitor signal output from a corresponding monitor sensor, and that controls the timing of the commencement of a subsequent accumulation of electric charges in said plurality of line sensors; and a signal output processor that reads the accumulated electric charges from said plurality of line sensors and then outputs image signals corresponding to an object image, said electric charge accumulation controller commencing accumulation of electric charges before said signal output processor finishes reading all electric charges in said plurality of line sensors, wherein said electric charge accumulation controller prohibits performing of a determination process that determines whether the monitor signal exceeds or reaches a threshold level, until the reading of image-pixel signals is finished.