This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Adjustment Of Release And Circuit Breaker. In order that the circuit breaker may be adjustable in height, the two slots C, C are cut in the vulcanite base, and this little instrument is attached to the side of the camera with wood screws. Practice has shown that it is quite safe to adjust this device so that contact of rods H and I is made at K when the lower edge of the mirror in the camera is on a line with the top of the lens.
568. Electric wires are fastened to the binding posts D, D, Figure 1, on the bed of the flash machine, and the other ends of these wires (O) attached to the binding post in the battery box. The ends of the wires (P), Figure 2, are also connected to binding posts on the battery box. These two sets of posts should be connected by means of a switch, which should be disconnected excepting when ready to make the flashlight exposures. The exact instant that the exposure is made can be easily determined by means of a one-half candle power incandescent lamp, to be held against the binding posts of the flashpan.
Caution. It is, of course, necessary to do this before placing either the fuse or the powder charge in the pan, to prevent accidents. This test, moreover, proves the soundness of all contacts and secures a prompt firing of the charge when operating. The completed apparatus is clearly shown in Illustration No. 45.
Making Exposure. Having thus prepared the installation, the camera is focused and the exposure made in exactly the same manner as if daylight were used, not forgetting, however, that the shutter must be set with its full sized opening in front of the plate, and not wound up entirely. The release of the shutter takes place immediately after the firing of the flash and stops the additional daylight exposure, if any. The lens opening should be regulated accordingly, and in its turn determines the quantity of flash powder. In the example illustrating this article a Goerz Dagor, Series III, No. 3, was used, with an opening of f. 12, the powder charge being 10 grains, as previously stated. The picture of the race-horse was obtained with a Goerz Celor, Series IB, No. 4, at its full opening of f. 5.
571. The electric flashlight, as described, is the invention of Mr. E. F. Keller, of New York, to whom we are greatly indebted for this valuable adjunct to the Reflex camera, of which he is an expert user.