One of the most noticeable features of modern dry plates is their intense rapidity. When a non-photographer reads that certain pictures of trotting horses have been taken in the 2,000th part of a second, he is apt to smile with incredulity. But he must be convinced in spite of himself that there is no exaggeration in the statement, if he be shown one of the many photographs which have been taken of lightning flashes. The duration of time represented by a flash of lightning is something infinitely less than the 2,oooth part of a second. But such pictures are, at the best, but scientific curiosities, although they prove most conclusively the intensely rapid manner in which a gelatine plate can be affected by the access of light.
Most beginners will not be content until they have tried their 'prentice hands at instantaneous work, although, possibly, they will soon learn that slower pictures which give more time for their consideration and general treatment, are as a rule far more satisfactory in the end. Still there are many subjects - such as sea-scapes with shipping, animal studies, including children (pardon us, fond parents) which must be taken instantaneously, or not at all.
For instantaneous work the hand is not quick enough to uncap and recap the lens. A piece of apparatus called an instantaneous shutter, is therefore employed to do this work automatically. Their number is legion, and the different designs show what a marvellous amount of skill has been expended upon this one item of the photographic outfit. We will content ourselves with noticing one or two forms of shutter only, but they may be regarded as being among the best in the market. First of all let us describe the "Phantom" shutter, shown at page 107. It consists of a light but strong frame of ebonite, with an aperture at the lower part, which fits the hood of the lens employed. In front of this aperture is a flap which can be either gently raised by the thumbscrew shown on the left hand side of the drawing, or can be suddenly released by touching the catch shown below. For non-instantaneous exposures, that is to say for all ordinary work, this shuttter can be usefully employed. The flap is slowly raised so that the dark foreground gets, as it should do, more exposure than the bright sky which acts so much more quickly upon the plate. When the flap is raised to a certain height, a shutter working in a grove suddenly falls behind it, and the exposure is terminated. For instantaneous effects the instrument is used in a somewhat different manner. An elastic band, shown in the cut, is fastened to the shutter and frame respectively, so that the descent of the former is rapid in the extreme. The tension of the rubber band also affects the flap which has a tendency to fly open unless held back by its catch. Directly this catch is turned to one side, or pulled to one side by an attached string, as shown in page 127, the flap flies up, and the shutter falls down.
The "Phantom" is rendered still more efficient by a mechanical attachment. This consists of a little pneumatic piston, with a tiny piston rod, which takes the place of the catch shown in page 127. In communication with the piston is a tube, which may be of any convenient length, terminated by an india-rubber air-ball. Pressure of this air-ball in the hand causes a force of wind to rush through the tube to the piston, the little rod is forced back, and the shutter does its work. It may be mentioned that this pneumatic attachment is the means adopted for working many other forms of shutters, one of which will be next described.
The "Right-about-turn" shutter (see two Figs. on page 127) has a certain likeness to the "Phantom," but it has the merit of being one half the size. It is thus described by the makers who claim that it is the lightest and smallest shutter made. "One screen opens as flap in exposing, then falls back upside down as a drop shutter in closing, giving foreground the longest exposure. The length of exposure is under complete control, slow or quick action being obtained either by pnuematic action or hand lever." One Fig. shows the first part of this action. The shutter has been released, and the flap is rising, slowly or quickly as the case may be. In the other it has risen completely and is commencing its downward drop so as to terminate the exposure.
In the "Economic" shutter (page 127) we have a flap which opens and closes again by a crank action with great smoothness and rapidity. The simplicity, as well as the small bulk of this contrivance must quickly render it a favourite. Even with the most compact apparatus, the tourist likes to reduce the weight of his necessaries as much as possible. The adoption of an instantaneous shutter which can be carried in his waistcoat pocket will be a sore temptation to him.