Suppose such an easy subject selected as we have mentioned ; we operate in the following manner : We take our standpoint and manipulate our camera as we would were we taking an ordinary landscape. We then put the dark slide in position, cover the camera with the focussing-cloth, and wait for the effect which we desire, which may be a certain formation of cloud in relation to the sea or river which we are photo graphing.
We then draw out the shutter of our slide, gently ease the cap of the lens till it is almost loose, then with a rapid motion lift it a few inches, and replace it. The exposure given should not exceed one-third or a quarter of a second, and will be quite brief enough to ensure the faithful rendering of a ripple on the water, or of any waves, except such as may be breaking violently on the shore.
For the majority of subjects which come under the heading of instantaneous an instrument usually desig nated an "instantaneous shutter" is required; and indeed, even for the subjects which we have mentioned, it will be found far more convenient to expose by the means of a shutter than by hand, although with a little care perfect results can be got by the latter method. The object to be effected by every instantaneous shutter is the quick opening and again closing of the aperture of the lens, so that the image of whatever is opposite the camera falls on the plate for a very brief space only.
The duration of so-called instantaneous exposures varies according to the subject. It is evident that the more rapidly an object is moving the briefer must the exposure be. For almost any subject an exposure of from one-fifth to one-twentieth of a second is brief enough, but for some special ones shorter exposures are necessary. In most instantaneous shutters there are provided means of giving exposures of various different lengths.
We here illustrate Cadett's patent pneumatic view shutter. This shutter fills all these requirements, for it will give exposures from the one-hundredth part of a second to any longer period of time without limit, and these results are obtained by the simplest of means •—a revolving ebonite disc, worked by a coiled spring in the centre, two catches, and with Cadett's pneumatic ap paratus. Five minutes' careful inspection will enable any one to work it.
Chadwick's patent view shutter, with Cadett's patent pneumatic apparatus, is a very serviceable one, and per mits an adjustment for various times of exposure, but not to such a full extent as Cadett's view illustrated above. It is simple, light, and easily adjusted.
Since we published the first edition of Marion's Practi cal Guide to Photography Mr. Cadett has invented a new shutter of most ingenious construction. We trate it here. The principle on which it works is as follows : The disc which is seen towards the top will, when a trigger is released by pressure on the pneumatic ball, revolve, performing a complete circle. As it revolves the pin which will be seen near its circum ference works in the slot of a rectangular shutter, which it lifts and again lowers, uncovering and again covering the lens in a marvellously brief space of time if desired. The little button which may be seen at the side of the instrument is for adjusting the tension on the spring which carries the disc round, so as to vary the length of exposure at will. Besides this there is an adjustment, by applying which the shutter will remain open as long as the pressure on the indiarubber ball is sustained, closing as soon as the pressure is relieved. This adjustment makes the instrument very useful for portrait work.
It should be mentioned that the shutter is made of ebonite, and that the moving part is so exceedingly light that, although the motion is a reciprocating one, the camera is not shaken even when the briefest exposure is given.
The method of using these shutters is simple. The point of view is selected, and the camera is fixed up and manipulated up till the time of exposure, precisely as for ordinary work, the only difference being that the instantaneous shutter replaces the lens cap.
The effect is again waited for. The shutter is set to give the length of exposure which is judged to be the best. Shortly before the expected combination of boats, ships, crowd of people, or whatever may form the picture, the shutter of the camera is withdrawn, and the photographer waits and watches with the pneumatic ball in his hand. At the correct instant he squeezes the ball, and the picture is taken.