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EXTERIOR LIGHTING
a final table, and opposite this number is found the exposure in fractions of a second, minutes or hours.
Based on the same principle as these exposure tables, various portable exposure meters have been brought out, in which scales representing the coefficients for plate-speed, light and diaphragm are arranged as in a slide rule, so that, when properly set, the normal exposure required can be found by inspection, and increased or diminished according to circumstances.
The Harvey meter and the Burroughs & Wellcome meter and handbook are for sale by every photographic supply house.
The Watkin's Kinematograph meter is fitted with a pendulum for counting half seconds and crank turns. It is made especially for motion picture operators and is about the size of a small watch. It gives a direct reading showing either the shutter opening or diaphragm number required under the given conditions. It is sold by Burke & James, Chicago, as are the Wynne meters described below.
G. F. Wynne's "Infallible" exposure meter is also in dial form, but the sensitive paper is exposed directly, no pendulum is used, and the scales are open on the dial. In use, the glass carrying the movable scale is turned until the actinometer time in seconds upon the exposure scale is opposite the diaphragm number of the plate, as given in the list of plate speeds ; the correct exposure will then be found against each stop given on the scale. There are practically only two scales ; the scale of diaphragms representing the diaphragm or f numbers, the speed of plate and the variation of exposure due to subject; and the time scale, representing the actinometer time and the exposure. The actinometer is protected by a yellow glass screen when not in use. In a smaller form the scales are on the circumference of a locket, and the actinometer at the back. An "Infallible" Printmeter is also made for showing exposures in contact printing on sensitive papers, but can also be used for testing speeds of plates and papers. Beck's "Zambex" Exposure Meter gives the exposure and stop to be used, also the depth of focus to be obtained with different diaphragm apertures. The required exposure is set to the "speed" number on the next scale of the meter. The third scale corresponds tb the times of darkening the sensitive paper in the actinometer attached to the meter, and shows the dia
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