GB1293608A - Photographic camera with focusing device - Google Patents

Abstract

1293608 Automatic focusing EASTMAN KODAK CO 18 Dec 1969 [23 Dec 1968] 61760/69 Heading H4D In a focusing system for a camera, light from a subject is directed along first and second parallel paths to separate photo-cells, the first path including a modulator and the second, unmodulated, path having its light transmission reduced to the mean of that in the first path so that decrease in the opposed outputs of the two photo-cells stops focus adjustment at the position of focus. In Fig. 1, light from a selected area of a subject to be cine photographed passes through the main camera lens, or, as shown, an auxiliary lens 14 to influence two photo-diodes 18, 24 by virtue of a beam splitter 16. The light falling on photo-cell24 is modulated by a disc 22 having alternate transparent and opaque sectors while a neutral density filter 20 is arranged to balance the output of photo-cell 18 to the average output of photo-cell 24. Focusing is initiated by starting an electric motor 40, Fig. 2, which adjusts the main zoom lens 10 from near focus towards infinity. The modulated output from the differentially connected photo-cells 18, 24 is applied through a band-pass amplifier 30, which eliminates the effects of ambient lighting variations, to one integrating circuit 34 which retains the peak value of the modulation and another integrating circuit 36 which follows the envelope of modulation amplitude as the focus changes. When the peak value reaches a maximum and the signal from integrator 36 begins to fall relative to the signal from integrator 34, a transistor comparator 38 produces an output to stop motor 40 at the desired position of focus.