SWING BACK.--A contrivance at the back of a camera which admits of an inclination of focusing screen, or dark slide, with reference to the axis of the lens. If the swing be confined to one plane it is a single swing back ; if arranged to move upon both a horizontal and a vertical axis it is termed a double swing back. For the same purpose other devices have been used, such as a moving or swinging front, etc.
The swing back is useful in nearly all branches of photography. In landscape work it is useful in bringing the foreground and distance into focus at the same time. To do this it is generally neces sary to employ a very small stop, which means a consider ably increased exposure. By moving the top part of the swing back in an outward direction, how ever, it is possible to bring both planes into focus. With a double swing back objects at any Dart of the plate whether at the top both tom, or sides, can be brought into focus.
In architectural photography the swing back is exceedingly useful although often abused. When it becomes necessary to tilt the camera to take in a large building the vertical lines will naturally all converge to the top, causing the houses to have a tumbled down appearance. By
means of the swing back, however, the back of the camera can be kept perfectly horizontal, and the lines will be straight In portraiture the swing back is also useful in bringing all the parts of the sitter into focus, without increasing the exposure, by stopping the lens.
The theory of the swing back is this : The nearer an object from which rays of light proceed, is to the lens, the longer will be the focus of these rays after they have passed through the lens, consequently those rays which proceed from distant objects have a shorter focus than those proceeding from a nearer point. By swinging the back of the camera it will not be difficult to see how it is possible to get both rays in fo cus at the same time and upon the same plane.
The simplest form of swing back is that in which the back of the camera is hinged to the baseboard. The most perfect form, however, is that in which. the back, whether swung horizontally or vertically, makes its own center the center of move ment. Figs. 451 to 454 show the various ef fects obtained by the use of the swing back. (See Burton's Photographic Optics, page 71.)