GB1191587A - Photographic Projectors. - Google Patents

Abstract

1,191,587. Photo-electric transparency position determining. EASTMAN KODAK CO. June 20, 1968 [June 23, 1967], No.29398/68. Heading G1A. The position of the front face of a transparency 20 Fig. 1 in a projector is determined by the photoelectric detection of the displacement of a pilot image 68 formed on the face by a source 26, and the objective lens 22 and either the image source or the detector 70 are moved by a reversible motor 58 in response to the displacement signal to refocus the system and eliminate the signal respectively, the system including means for disconnecting the error signal from the motor, clamping the moveable source or detector source member, and connecting a source of polarized signals to the motor to move the objective lens 22 as required. Friction couplings 40, 42 are provided in the lens drive, and a knob 38 provides for manual positioning gear wheels 44, 34 having a 2:1 ratio so that the signal is nulled when the lens is in focus. The path to the detector 70 includes an infrared pass filter to increase the sensitivity. The detector comprises a centretapped photo-conductor arrangement 80, 82, Fig. 2 in a bridge circuit and the differential output due to displacement of the image beam, energizes motor 58 through one or the other two stage transistor amplifier arrangements A or B. Capacitors 84, 86, in the bridge circuit boost the initial motor movement and, as the null position is reached introduce braking. Remote control of the objective lens position is provided by a switch 144 and the servo-control circuit is opened by a reed relay 164, electro-magnet 74, effecting the clamping of the movable image component support. Reference is been directed by this Comptroller to Specification 1, 016, 567.