[Fig. 425]
A 2-1/4 x 3-1/4 film pack adapter or a 2-1/4 x 3-1/4 cut film holder holds the film in the camera. The film pack adapter will hold a pack of 12 sheets of film, and accordingly, will permit the taking of 12 pictures. The cut film holder is a unit which holds two sheets of film utilizing each side of the holder.
It is pointed out that the FBI uses the film pack exclusively in view of the fact that practically all latent examinations will necessitate the taking of more than two pictures. Further, the film pack is made so that it may be loaded into the adapter in the open light. Also, the films are numbered 1 through 12, which is a valuable feature in that in maintaining notes concerning the latent examinations it is a simple matter to note by the number of the negative where the latent impression was developed and photographed. Should it happen that during a latent examination all twelve of the films are not used, the film pack, with the slide in place, is taken into the darkroom and only those films which have been exposed are removed and developed. The unexposed films remain in the film pack adapter with the slide in and may be used later.
As was previously mentioned, the camera has a fixed focus; that is, the camera will take a legible picture only when the latent print is at the focal point, or exactly flush with the opening of the camera. The latent print must not be inside the open end of the camera, nor must it be beyond; otherwise, the picture will be blurred.
Since the camera has its own light source, any leakage of outside light will cause overexposure of the film. Consequently, if the surface of the object bearing the latent print which is to be photographed is uneven or does not cover the entire front of the camera opening, it will be necessary to use some opaque material such as a focusing cloth or heavy dark material to cover the front of the camera so as to exclude all outside light (fig. 426). If a latent print on a pane of glass or an automobile window is being photographed, it will be necessary to back up the latent so that there will be no light leakage. Material showing a pattern or grain should not be used for this purpose as any such pattern will photograph in the background and possibly obliterate the ridges of the latent print.
[Fig. 426]
To insure an equal distribution of the light over the latents being photographed, the impressions should be centered in the opening of the camera. This is accomplished by opening the angular front section of the camera after the metal plate covering the front has been opened, and setting the aperture over the latent impressions so that they will be as near the center as possible. Then, holding the camera firmly in place, it is carefully closed (fig. 427).
[Fig. 427]