Early Work In Photography
A Text-book For Beginners

42 Early Work in Photography. position at will, and the change should be effected almost instantly; this does away with the old clumsy method of unscrewing the camera from the tripod head, and screwing it down again in another position. Double extension provides for the use of either short or long focus lenses,and in a whole-plate is an absolute necessity. Most modern cameras are built to accommodate lenses of widely different foci; as a general guide a whole-plate camera should be adapted for use with lenses of from five to twenty-three inches focus—such an extension will pro- vide for extreme requirements. Another feature to note in choosing a camera is to see that the focussing is effected from the front, i.e., that the front of the camera is movable, while the back parts (containing the focussing screen) is sta- tionary. In some cameras the focussing may be effected from the front, and the back also is movable; when using lenses of Circular Level. short focus this is a great advantage, as it avoids any possi- bility of the front of the base-board coming within the field of the lens. The sensitive plates are carried ready for exposure in a small light-tight chamber. The plate lies flat in this chamber, and its face is covered by an opaque lid or cover, sliding in grooves. This chamber fits tightly on to the back of the camera in the same position as was occupied by the ground glass, and enables the photographer to insert the plate into the camera, and withdraw the protecting cover from the outside, without admitting light. The lens is covered during this operation, as will be ex plained ; of course, directly the lens is uncovered, the image falls upon the plate, until the lens is again covered, this constitutes the exposure; the cover is then replaced over the exposed plate, so that it can be removed from the camera. These chambers each carry two plates, and are