04494839 is referenced by 6 patents and cites 4 patents.

An automatic focusing device for slide projectors in which at least one photo-electric receiver of the secondary projection device which determines the position of the slide generates, from a beam of light impinging upon the receiver, the error voltage controlling the focusing of the slide. The error voltage is fed into an electronic amplifier circuit of the focusing device, which contains manual facilities for refocusing the slide comprising primary switching elements which automatically apply the error voltage produced by the photoelectric receiver to the positioning motor for the focusing device, but only when this error voltage reaches a predetermined level. In addition, the device contains secondary switching elements which cut off the amplifier circuit from the positioning motor when the manual facilities for focus adjustment are operated, and which connect the focus adjustment means to the positioning motor and adjust the positioning motor to run at a constant speed via a combination (group) of resistors.

Automatic focusing device for slide projectors
Application Number
Publication Number
Application Date
February 24, 1983
Publication Date
January 22, 1985
Dietrich Brueckner
Schwartz Jeffery Schwaab Mack Blumenthal & Koch
Ernst Leitz Wetzlar
G03B 3/10
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