[General photography]
In the foregoing instances in which it has been impossible to obtain suitable inked impressions it will be noted that the last resort has always been photography. In all probability in advanced cases of decomposition, desiccation, and maceration it may not be possible to secure inked impressions which can be properly classified. Hence, it will be necessary to photograph the ridge detail. Accordingly, there are outlined below several methods of photographing the ridges which have been used with success.
In photographing the ridge detail on fingers it has been determined to be most practicable to photograph the finger natural, or 1/1, size inasmuch as comparisons will usually be made with inked impressions which are natural size. Any camera built or adjusted to taking 1/1 size pictures, and with which the lighting may be arranged to best advantage, may be used.
There is a wide choice of film which can be used for this purpose. The so-called soft films are all good for photographing ridge detail on fingers. Process film is not recommended inasmuch as the film presents too much of a contrast. Consequently, if it is used, some of the ridge detail will be lost, especially if wrinkles are present in the skin.
Lighting is accomplished by the use of gooseneck lamps, floodlights, or a spotlight. If a fingerprint camera is used, its lights may be sufficient.
The manner of lighting may be by direct light, side light, transmitted light or reflected light, depending upon the prevailing condition of the finger or skin.
Direct light is used in those cases in which the ridge detail is fairly clear and there are no wrinkles present; or, if wrinkles are present, they are not deep enough to interfere with photographing the ridges.
Side lighting is used when there are no wrinkles of any consequence and the ridge detail is clear but because of discoloration the ridges are not readily seen in the ground glass as there is lack of contrast between ridges and depressions. Accordingly, the lights, instead of being focused directly on the skin or finger, are placed to the side of the object so that the light is directed across the skin or finger, thus highlighting the ridges and shading the depressions.
In side lighting, two lights may be used. Better results are often obtained, however, by using only one light, such as a spotlight, the beam of which can be controlled to best advantage.
Transmitted light is used in cases in which the skin has peeled off or in which the dermis has been removed, cut, and scraped thin so that light will go through. The prepared skin is placed between two pieces of glass pressed together in order to flatten the skin or dermis and remove creases. By trimming some of the surplus skin or dermis, especially at the top, it may be more easily flattened. After the glass is properly mounted in front of the camera, the lights are placed behind it and light is directed through the skin. The ridge detail is brought into focus on the ground glass. Before the picture is actually taken it is suggested that the ground glass be checked by first using one light and then two lights to see which is more effective.