EXPOSING, METHODS OF The usual methods of exposing dry plates in a camera are by means of a cap or shutter. The cap method was the original one, and although it is considered old-fashioned it still has advantages. In landscape work the cap may be made tp serve as a lens shade by holding it above the front of the lens during exposure. The correct way to uncap a lens is to imagine that it is hinged to the top of the lens hood. The cap is loosened by twisting and the lower edge raised until it is clear of the lens, and replaced again when exposure is finished ; in this way the cap not only serves as a lens shade, but, by raising and lowering at a suitable speed, one can give more exposure to the foreground than the sky, and at times obtain clouds on the negative which would be missing on account of over exposure if the sky had the same amount of exposure as the landscape.
By the judicious use of a cap one may picture a busy street as being empty, and such a method is sometimes handy when one desires a photo graph of a building in a busy street without showing the traffic. The lens in such a case is stopped down to its very smallest extent, the smaller the better, so as to require a very long exposure, the longer the better ; exposure is then made by a series of very brief exposures with a cap. Assuming, for example, that an exposure of one minute is considered to be necessary, the plate is exposed for two seconds and the cap carefully replaced, another two seconds is given, and so on until the plate is considered to be fully exposed. The brief
exposures will not be enough to picture moving objects, and only those which have remained still during the greater part of the minute will show when the plate is developed.
Shutter exposures are invaluable in cases of portraiture, and of course absolutely necessary for instantaneous work, as the quickest " off and on " cap exposure possible is estimated to be one-fifth of a second, but in the majority of cases it is nearer half, or even a whole, second. Silent-working shutters, preferably those which work inside the camera, are the best for por traiture, as those which work noisily and outside the camera are apt to startle the sitter, or other wise attract attention at the wrong time. Chil dren, for example, when posed in a position looking away from the camera, will. often turn their heads when hearing the click of the shutter. When exposing for portraits and giving a time exposure with a roller blind shutter, it is a good plan to pull the cord gently so as to raise the blind and to release it before it reaches the half way click, at which it remains open ; the spring will pull the blind down again if the click is not passed, and in this way an absolutely silent exposure may be made. For exposures for self portraiture, printing, enlarging, etc., see under those headings, and also " Exposure Tables."