Image pickup apparatus and method and system for controlling the exposure of the image pickup apparatus

Disclosed are an image pickup apparatus and method and system for controlling the exposure of the image pickup apparatus. The image pickup apparatus includes a circuit for detecting a voltage corresponding to a current value of an iris, a circuit for generating a voltage corresponding to a desired iris value, a circuit for comparing the two voltages, and a circuit for controlling the iris based on the result of the comparison so as to keep the iris value at the desired value, in which the exposure start time of an image pick-up device is changed in an increment/decrement of one horizontal scanning period and/or in an increment/decrement of a period shorter than one horizontal scanning period to thereby make it possible to perform manual-iris mode automatic exposure control.