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446 HIGH-SPEED PHOTOGRAPHY November
which were rated at 100 volts. When they were set up on the subject, two lamps burned in series so that each lamp burned at approximately 60 volts. In the case of the Fastax camera when the shadow density was observed through the ground glass with this setup and by stopping down the lens, an exposure would be correct for 5000 pictures per second at between //5.6 and//8 depending upon the color and brightness of the subject. This guessing method has not been too satisfactory. When they were ready for picture-taking the lamps would be turned on to full brightness and used in parallel rather than series. There is available on the market today a very convenient series-parallel switch for this purpose, as well as for a new lamp which will be mentioned shortly. It is manufactured by the Industrial Timer Corporation, Newark, New Jersey. This particular switch will accommodate four lamps and is known as their "HI-LO" switch.
There has been recently developed by the General Electric Company a "750R" high-speed photographic lamp. This particular lamp is designed to operate at about 18 inches from the subject and the candle power at that distance within 5 degrees of its axis is 75,000. Two of these lamps are adequate to make pictures of subjects up to 4 by 4 inches at//5.6 at 5000 pictures per second. Using four of these lamps on the subject it is possible to take full-color Kodachrome pictures at 5000 pictures per second at //2.
Mercury-arc lamps have not been satisfactory on alternating current because of their pulsing on and off. The Philips Company is using mercury arc for illuminating subjects powered with direct current so as to avoid flutter. Fluorescent lamps cannot be used because of their fluttering and comparatively low intensity. One should consider that between approximately 100,000 to 500,000 footcandles are necessary to take pictures under ordinary circumstances of high speed with the lens reasonably well stopped down.
In order to eliminate many of the troubles that have been encountered, the Weston Electrical Instrument Company is announcing an exposure meter for high-speed photography which will measure either incandescent light or sunlight. Edgerton earlier announced a high-speed gas-discharge-tube exposure meter. There will be provided an index on the Weston meter for measuring values of light from 100 to 300,000 foot-candles. Three steps on the meter will be necessary in order to measure this range, and there will be attached to