FIG. 1.—AMATEUR’S CHRONOPHOTOGRAPHIC APPARATUS.
The experiments which we have been describing necessitate apparatus of the most expensive kind, and they are unadapted for the use of the amateur. The apparatus of M. Georges Demeny, which we [illustrate], is, however, very simple. The reader needs to be reminded that there are three types of chronophotographic machinery in use, in two of which a single objective, with a disk shutter revolving at great speed, is employed. In one the object shifts, and gives several images from an immovable plate, while in the other the object is stationary, and the movable sensitized surface gives well-separated images. The third method, which is the least interesting, consists in taking as many objectives and plates as it is desired to have images, and in freeing the shutters of each objective, one after the other. The most scientific solution of the problem is that which permits of obtaining upon a band of film, and with a single objective, a succession of well-separated images whose number depends only upon the length of the band employed. The difficulty in using a sensitized band consists in arresting it for the very brief instant in which each image impresses the plate. The Demeny apparatus which we are about to describe is very simple. A wooden box having about the dimensions of an ordinary seven by nine inch apparatus is provided with an objective of wide aperture, of which only the center is utilized. Back of this objective, and as near as possible to the sensitized surface, the disk shutter is revolved by means of a crank. Up to this point there is really nothing new in the apparatus; but the principal improvement consists in the unwinding and arrest of the sensitized film. Number 1 of our first [engraving] represents the principle of the system. Two disks, R and P, are each mounted upon an axis passing through their centers; bobbins that carry the films are fixed, one of them at R, upon a spindle mounted in the axis of rotation of the disk, and the other at P, upon a spindle mounted eccentrically to such axis. It is this eccentric position that chiefly constitutes the invention. Let us suppose that the two bobbins are in place, as shown in cut. The film wound upon A, having one of its extremities attached at B, follows the course, C, S, during which it passes behind the objective; the two bobbins cannot have any proper motion in consequence of the method of fixing which is adopted; they and the disks, R and P, that support them, become interdependent. Because the disk, P, revolves, the film coming from A will wind around B; but, in consequence of the eccentric position of this bobbin upon the disk, traction will cease to occur for a very brief instant at the moment at which the bobbin, B, approaches A as closely as possible, Despite this, as the winding always proceeds to a degree proportional to the unwinding, the film remains perfectly taut. It is at this moment that the window, H, of the disk, L, uncovers the objective for an instant. It will be understood that the crank, M, sets the disk in motion, and it is this, through a mechanism of gears, that controls the operation of the bobbins. There is, therefore, an exact mathematical coincidence between the arrest of the film and the passage of the window, and this is essential for the sharpness of the image. This would not always occur if a friction device was depended upon for the rest of the film, for in this case a sliding might occur which would produce a blurring of the image. The solution offered by the Demeny apparatus is, therefore, the simplest and one of the surest known. The simplification of the mechanism has permitted of constructing an apparatus light enough to allow of operating without a tripod, by holding it in the arms, as shown in our second engraving. Each film terminates in a strip of black paper glued to it, and forms a complete covering after the winding upon the bobbin. This arrangement protects the sensitized part from the light, and permits of changing the bobbin in daylight. Twenty of them can be stored in the spaces in the box left by the mechanism, so that one may always have a large supply on hand.
FIG. 2—METHOD OF USING THE
DEMENY APPARATUS.