The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Self-Toning Papers                         Shutters, Instantaneous
Self-Toning Papers. Two classes of paper sold under this name have come into rather general use during the past four or five years. One class contains gold, this metal acting as an ordinary toning agent, and the other class contains both a silver salt and a ferric salt. On this latter a faint image is produced by exposure, and this becomes intense when the paper is wetted, by reason of the reaction of the ferrous salt which is formed, with the excess of silver salt. (See Catalysotype.)
Sensitiveness, Sensitometry. See Exposure.
Shutters, Instantaneous. When the images of rapidly moving objects are desired, it is found that the hand is not quick enough to uncover and recap the lens, therefore some mechanical device is used for this purpose, and is called an instantaneous shutter. The names, styles, and prices of these are legion, but they may be conveniently divided into two main classes: (I.) Exposing Shutters; (II.) Rapid Shutters. As some practical guide, the following notes on each form are given: -
(I.) Exposing Shutters. These are more or less simple arrangements devised to replace the cap, and are usually fitted
Fig. 114.
to the lens hood and actuated by a pneumatic ball and tube, which releases that portion of the shutter covering the lens, and again covers the objective when the necessary exposure has been given. Usually pressure on a ball, or the tension on a string or cord, raises a flap from in front of the lens, which remains raised to such pressure or tension is removed when the necessary ex-posure has been given. Many of the shutters classed in Sec-tion II. are arranged to give time exposure also.
(II.) Rapid Shutters. This class may be again conveniently divided into (a) shutters working in front of the lens, (b) those