MOVEMENTS AND FITTINGS OF THE CAMERA.
For general photographic work the camera should have the following move ments : A double extension—that is, both a sliding board or frame and an extending base. The total extension should be equal to or greater than twice the diagonal of the plate to be used with it ; 18 in. for half-plate, or 12 in. for quarter-plate. There should also be an extra movement moving the camera, is necessary. A camera that must be placed on its side, or in which the slide must be fastened with turn-buttons in order to effect this, is old-fashioned. Focussing should be clone by rack and pinion, and, if the camera is to be used for copying and other indoor work, it is better that the focussing should be done by moving the back part. Conical bellows cameras are usually more compact, but for general work square bellows should be chosen. A small circular spirit-level of back or front, making it possible to bring the lens and the plate close together over the centre of the base, for use with short focus lenses. The frame carrying the dark-slide or plate-bolder should be movable, so that it may be placed at an angle to the front. This is called a swing
back. Not only should it swing back wards or forwards, to bring the plate up right when the camera is tilted either up or down, but it should swing from side to side, to accommodate the focus. The lens should be capable of being moved up and down and clamped firmly in any position. This rising front is far more essential than a sliding front, or move ment from side to side. A reversing back, which makes it possible to place the slide (which should run in grooves) in either a vertical or a horizontal position without should be attached to the top of the back frame, and a plumb indicator to the side of the swing hack. It should be seen that these are correctly and truly fitted, as otherwise they are worse than useless. The dark slides should be of double book form, and in accurate register with the focussing screen. There should be no loose parts. Figs. 21 to 28 show typical field cameras, having distinctive features, all being serviceable and each one excellent for special purposes.