GB512817A - Improvements in photographic exposure calculators - Google Patents

Abstract

512,817. Photographic exposure calculators. GROVES, W. W. (I. G. Farbenindustrie Akt.- Ges.). March 23, 1938, No. 8911. [Class 106 (i)] [Also in Group XX] In calculators of the type in which the exposure time is determined by turning a selector dial once for each factor, the dial returns automatically to its original position after the manner of the dialling mechanism of automatic telephone apparatus and optical or acoustic devices are provided to warn the operator against possible errors in manipulation. Preferably a window is provided in which the next operation to be performed is indicated after each step. Means may be provided to lock the mechanism after the requisite number of operations. The apparatus may be returned to initial position by pressure on a knob. In the form shown, the dial 2, Fig. 1, is provided with a series of numbered holes in which the finger is inserted in accordance with numbers derived from the tables T, the dial being then rotated till the finger reaches the stop 5. Rotation of the dial turns the bell .crank lever 3, 4, Fig. 3, the arm 3 advancing the ratchet wheel 6 to bring a different instruction behind the window 7. The arm 4 advances the ratchet wheel 11 which drives. the time -scale wheel 8. The dial is returned to initial position by a spring in the housing 12<SP>1</SP>, the wheel 8 being prevented from reverse rotation by a brake spring 13<SP>11</SP> engaging a tooth on the wheel 12. After the series of selections is completed, a pin 26 on the wheel 6 engages an arm 29 to rotate the shutter disc to open the apertures 30 to disclose the times of exposure corresponding to the aperture values on the scale 36 and at the same time to ring the bell 31. The mechanism is released by pressure on a knob 39, the wheels being provided with 'return springs. The knob 39 may operate a counter. The apparatus may be coin freed.