A METHOD AND APPARATUS OF CONTRAST-DEPENDENT SHARP FOCUSSING

摘要

A method of performing contrast dependent sharp focussing of an optical system. Light is direct via an object lens through an image field diaphragm and rotatable optical wedge. A measurement area is defined which is scanned by the optical wedge in combination with a photoelectric receiver behind the measurement area. The photoelectric receiver provides a variable frequency output signal in dependence upon the brightness/darkness distribution within the measurement area, which signal is processed by an electrical circuit to provide a frequency dependent signal which is used to automatically or semi-automatically adjust the position of the object lens to provide sharp focussing.