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.
Operating The Shutter. The Rotary Shutter shown in Illustration No. 5 is automatic in action and always set. It is operated by pressure on a lever, which protrudes from the side of the box. To obtain an instantaneous exposure one pressure of the lever will open and close the shutter simultaneously. By pulling out a small bar or lever projecting from the side of the camera the shutter can be used for time exposure. To obtain a time exposure two pressures of the lever are required - one to open the shutter, admitting the light through the lens, and another to close the shutter, cutting off the light. The diaphragm openings are conrolled by a lever in a similar manner to the time exposure.
54. The Single Valve Shutters (See Illustration No. 6) are provided with a dial and a pointer, the dial being marked T, B, I. When the pointer is turned to the letter T the shutter is then set for what is termed a bulb exposure; the lever or one squeeze of the pneumatic bulb will open the shutter, and a similar movement on the lever or bulb will close the shutter. If the pointer be turned to the letter B, the shutter is then set for what is termed a bulb exposure; that is, the shutter will remain open just so long as the lever is held down, or a pressure is exerted on the bulb. Releasing either will instantly close the shutter. The use of the bulb exposure is more particularly for photographing objects which are liable to move, and with which more than an instantaneous exposure is permissible. The I on the dial signifies instantaneous, and when the pointer is adjusted to this letter the shutter will work instantaneously when the lever or bulb operates it. The duration of the instantaneous exposure with these shutters is about equivalent to 1-33 of a second.
55. The Double Valve Shutters are similar in their work to the single valve shutter, but are more accurately adjusted and supplied with a greater range of movement. Usually the dial is provided with T and B markings, and from 1 second to 1-100 of a second. To obtain the various exposures the pointer is set to the letter or fraction of a second required. In Illustration No. 7 is shown a standard type of double valve shutter. This shutter is fitted with two levers, lever C on the right used for setting the shutter, while the lever D on the left is used to release it to make the exposure. The shutter is fitted for a bulb and tube with which the exposure can be made instead of with the finger release. The tubing should be attached to the valve on the left side. On the top of the shutter there is a small dial, containing the letters B and T; the dial is also marked in figures from 1 to 1/100, representing seconds and fractions of a second. When the dial, A, is turned so that the indicator, E, is placed at T it means time exposure. To set the shutter pull down lever, C. After setting the shutter, one pressure of the bulb or pressing down on the lever or finger release, D, opens the shutter and it remains open until the bulb or finger release is again pressed, when the shutter is closed. Timing exposures. When the dial is placed at B the shutter will remain open as long as the hand presses the bulb or the finger holds down the finger release. It is advisable to use B, or the bulb, for all exposures ranging from one-half to two seconds, as it is more simple to operate. For all expos-ures requiring longer time, the T or time exposure should be used. By pressing the bulb once, the shutter is opened and remains open until you again press the bulb when it closes, thus allowing for any length of exposure. When instantaneous or quick exposures are required, then the dial
Illustration No. 5.Rotary Shutter.
See Paragraph No. 53.
Illustration No. 6.Single Valve Shutter.
See Paragraph No. 54.
Illustration No. 7. Double Valve Shutter. See Paragraph No. 55.
Illustration No. 8.Automatic Shutter.
See Paragraph No. 56.
should be set at 1-100, 1-50, or 1-25, which indicate fractions of a second. The proper one to use depends on the strength of light. In real bright light 1-100 is best, and in medium light 1-50 or 1-25. When set at 1-100, which is the quickest exposure that can be made with such a shutter, one pressure of the bulb or pressing down of the finger release will make an exposure 1-100 part of a second. When the dial is placed at 1-50, 1-25, 1-5, or 1-2, one pressure of the bulb or pressing down the finger release will give the indicated fraction of a second exposure. To focus the camera turn the dial at T, set your shutter by pressing down the finger release, C, opposite the side from which your tube is attached; then, one pressure of the bulb will open the shutter and permit you to see the image on the focusing screen (ground-glass).
56. Automatic Shutters are made of the single valve and double valve type, and also without any visible valve, and are termed automatic for the reason that they are always ready for exposure without having to be "set," as the older forms of single and double valve shutters have to be. The automatic shutter can be seen to have its advantages over the older forms, but at the same time greater care is necessary in seeing that the shutter is not opened inadvertently through a pressure of the bulb, which could not take place with the older shutter before it was set. In Illustration No. 8 is shown a common form of double valve automatic shutter which automatically sets itself after each exposure. The setting of the speed in this class of shutter is practically the same as for the one shown in Illustration No. 7. An indis-pensible part of all between-the-lens shutters is the diaphragm or stop, which regulates the quantity of light passing through the shutter to the plate or film.