Automatic focusing apparatus including image contrast detection means

Abstract

Disclosed is an automatic focusing apparatus for an optical imaging system which utilizes a focus detector which monitors the contrast of the image at the focal plane of the imaging system, the image being deemed to be in focus when the contrast of the image is maximized. The focus detector comprise a plurality of detector/converter elements arranged in an array in the focal plane. Each detector/converter senses the light intensity in a respective portion of the image at the focal plane and provides a pulse signal having a pulse-width which is approximately inversely proportional to the sensed light intensity. A detection circuit receives the pulses provided by the detector/converter elements and derives a digital quantity which is related to the difference between the maximum and minimum pulse-widths of the pulses. The digital quantity is received by a digital servosystem which appropriately adjusts the focusing of the imaging system to maximize the digital quantity provided by the detection circuit.

Dependencies are inferred from the claim text.