The invention an optical system and a method for automatically controlling the gain of a receiver in an optical system. The optical system includes an optical receiver, a pulse capture unit, and an automatic gain control. The pulse capture unit includes a capture unit capable of capturing an optical signal received by the optical receiver; and, a process unit capable of processing the captured optical signal. The automatic gain control is capable of controlling the gain of the optical receiver responsive to the content of the processed optical signal. The method includes comparing the intensity of at least one returned pulse, and typically a plurality of returned pulses, to a predetermined value; and controlling the gain of an optical detector responsive to the comparison. In addition, the maximum gain is controlled by a noise limit in some implementations.