Oblique lighting may be necessary to show up certain moulded impressions (such as those found in soft putty) or pick-ups. Inked impressions on cards or forms can be copied satisfactorily on a process camera, or by means of xerography in the case of good clear impressions. Filters can be of great assistance in rendering the background darker or lighter. This eliminates some of the intermediate stages in the preparation of the final print. When dealing with light impressions on a dark background, a camera fitted with a prism or optical mirror can be used. Some of the specially made instruments use electronic flash.
The fingerprint camera is normally battery-operated using four built-in bulbs. Illumination can be by daylight, photoflood, other tungsten light or by flash. Occasionally, 35 mm cameras are used but are not generally favoured. Special fingerprint cameras have the lens set at a fixed distance from the film and the impression, again to give an actual size image. When conditions are suitable, a technical double extension camera (stand camera) enables the impression to be recorded in actual size. Many are in difficult positions requiring some ingenuity on the part of the operator to get his camera into position. The equipment used varies according to the location and article on which the impressions are found. The surface on which the fingerprint impression is being photographed will determine aspects of the photographer's technique.
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