GB1510941A - Apparatus for photoelectrically determining the position of the focal plane in an optical system - Google Patents

Abstract

1510941 Photoelectric determination of a focal plane ERNST LEITZ WETZLAR GmbH 15 Jan 1976 1525/76 Heading H4D Apparatus for photoelectrically determining the position of the focal plane in an optical system comprises means 1-4 for imaging an object on at least one spatial frequency filter acting as or in combination with at least one photoelectric receiver system, the or each system being arranged to receive light fluxes and comprising at least one line of receivers, the apparatus further comprising electrically operable means to interrogate the receivers in pairs, means to evaluate the signals derived from the interrogation and means to indicate the focal condition of the optical system. In the embodiment of Figs. 1 and 3, corresponding ones of two lines 5, 6 of photodiodes are scanned simultaneously by means of shift registers 16, 17 controlled by a clock 25, the results of successive scans being fed to a differential amplifier 26, a rectifier 27 and means 28 for indicating the sum of the absolute differences between the signals from the diodes of each pair. If only one line of diodes 11, ..., n is used, Fig. 2, adjacent pairs are interrogated by transistor pairs 18, 19 etc. under the control of a single shift register 16'. Either a minimum or a maximum reading by means 28 will indicate an in-focus condition, depending on the relationship between the image, means 1-4 and the photodiodes. In these embodiments the photodiodes act as a spatial frequency filter. A separate spatial frequency filter may be provided in the form of an oscillated grating 29, Figs. 4, 6 (not shown) or gratings 29a and 29b, Fig. 5 (not shown). Light from the gratings passes to the photodiode system(s) and is evaluated as before.