" INSTANTANEOUS " PHOTOGRAPHY The term " instantaneous " is loosely used in photography, being generally understood to refer to exposures of less than one second. The photographing of ordinary views " instanta neously " was vainly attempted by Daguerre in 1841, and the first authenticated "instanta neous " photograph is that of New York harbour, taken in 1854 The essential conditions under which " in stantaneous " exposures, in order to be success ful, must be made are : A good light, an efficient shutter, a suitable lens working at a large aper ture, and a rapid plate. For average street work of a second is quite fast enough ; while if objects are moving to or from the camera direct and not at right angles, the exposure may be increased to nth of a second. According to the Thornton-Pickard Company, the following rule answers for finding the " instantaneous " expo sure for a moving object :The distance of the object from the camera, measured in inches, is divided by the number of yards per hour at which the object is travelling, multiplied by the focus of the lens in inches. The result will be
the fraction of a. second, which is the longest allowable exposure that does not show move ment in the resulting photograph. Below is given a table showing the correct exposure for various moving objects. The table is made out for a distance from the camera ioo times that of the focus of the lens : that is, for a 6-inch focus lens at 5o ft., a 7-in. at 58 ft., etc.
Towards the At right an Camera files to Camera (sec.) (sec.) Man walking slowly, street scenes .. Cattle grazing .. A ..
Boating Man walking, children playing, etc. .. Pony and trap, trot ting .. .. Cycling, ordinary aiff Man running a race, and jumping .. .. Cycle racing :au Horse galloping Th fr - 13i15 If the object is twice the distance, the length of allowable exposure is doubled, and vice versa. (See also " Focal Plane Shutter " and " Hand Camera, Work with.")