GB555275A - Process photographic (wet plate) exposure meter - Google Patents

Abstract

555,275. Calculating-apparatus. WARNE, J. Feb. 12, 1942, No. 1879. [Class 106 (i)] [Also in Group XX] A device for calculating the exposure time and the distance between the screen and the sensitized plate to be used in making half-tone negatives comprises a base member, Fig. 1, and a rotatable member, Fig. II, pivoted to it, the base member bearing an arcuate scale d representing the classification of the copy and two series of graph curves a, b representing respectively the lighting power and the screen ruling, and the rotatable member carrying two series of scales c, b<SP>1</SP> which represent respectively exposure times and screen distances and extend in both cases along radial lines each of which corresponds to a given ratio of enlargement or reduction. A series of arcuate guide lines co-operating with the graph curves extends over each of the radial scales c. b<SP>1</SP>. In use, the pivoted member is set so that its diametral edge indicates the copy classification factor an the scale d on the base member. The main exposure times corresponding to a given lighting power and a given ratio of enlargement of reduction is then given by the intersection with the appropriate radial scale of the arcuate guide line which at the diametral edge of the pivoted member is nearest to the graph curve indicating the lighting power. The correct screen distance is similarly obtained. The device also bears tables indicating "flash" exposure times and stop values and dimensions, and also conversion scales for indicating corresponding exposure time for plates of different speeds.