GB625988A - Improvements in and relating to photographic exposure meters - Google Patents

Abstract

625,988. Photographic exposure meters. MACADIE, H. S., and AUTOMATIC COIL WINDER & ELECTRICAL EQUIPMENT CO., Ltd. April 2, 1947, No. 8966. [Class 98 (i)] [Also in Group XL (b)] In an exposure meter of the kind described in Specification 458,546 in which a knob 27 carrying a scale of exposures which are read against a fixed scale of apertures gives a non- linear movement to a pointer 24 to bring it into coincidence with the pointer 22 of a photo-electrically actuated galvanometer, a light-reducing shutter comes into action when the pointer 24 is brought to one extreme position and is withdrawn when it is brought to the other. After an initial setting of the exposure scale relatively to the knob in accordance with the emulsion speed, the knob is rotated, driving cam 26 to give appropriate motion to pointer 24, by means of a bar 33 engaged by pins 35, 30 on the cam and knob assembly respectively and held by an S-shaped spring with the pin 30 at either end of a slot 31. In the extreme clockwise position, the cam comes up against a stop and further rotation of knob 27 brings the pin 30 to the other end of the slot. At the same time the arms of a U-shaped member 72 are engaged by ramps on the knob assembly so that the member moves axially and rocks a lever 55, Fig. 11, to bring a shutter 52 between the window and the photocell 20. At the extreme counter-clockwise position, the converse operation takes place. The position of the cam in relation to the knob is shown by an arrow 81 on a bolt 80 which holds the parts together and is unable to rotate relatively to the cam. If the bar 33 sticks in the dead-centre position it is moved into correct position, as soon as the knob 27 is turned, by engagement of a nose on the bar with one of two fixed stops 67, 68. According to the Provisional Specification, U-shaped member 72 may be replaced by a pair of balls mounted in holes in the cam.