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There is no great difficulty involved in photographing river and sea fish under controlled conditions in a suitable glass-sided tank. This may be either a fair-sized tank with a movable glass plate with which the subject can be penned into a narrow space, or the tank itself may be made narrow enough in the first place. A convenient tank for this is 2 feet long by 18 inches high by as little as 4 inches in depth.
When photographing small fish, the lens is generally brought up so close to the subject that there is very little depth of field. Under these conditions, the narrower the tank the better, because fish have a tantalizing habit of keeping beyond the zone of sharp focus if they are allowed the necessary freedom.
The tank must be fitted with the best polished plate glass, front and back, to prevent optical distortion. All stones, sand and water-weed that form the scenery inside the tank must be well washed. Unless this is done, the soil and dirt will be stirred up by the movement of the fish and degrade the quality of the picture. For the same reason, the fish and the water are always allowed to settle for an hour or so before taking any photographs.
The camera is never set up exactly square with the front of the tank or it would photograph its own reflection as well as the fish. It is moved about 2 inches to the side so that the lens-subject line is at an angle to the front of the tank. The small shift out of the square-on position makes practically no difference to the focusing of the camera, but it keeps its reflection out of the picture. All other reflections from the front of the camera and its surroundings are cut off by supporting a sheet of dull black paper or fabric opposite the front of the tank and just clear of the camera lens.
These precautions are, however, not necessary if the camera is brought up to the glass so that the lens hood actually touches it.
Fish may be photographed successfully indoors with artificial light. Again care must be taken to arrange the tank and lighting so that no reflections are shown in the glass, for a tank filled with water can act as a very effective mirror. Most of the front reflections may be obviated with a black cloth as already mentioned. Two floodlights set up above the camera and about 3 feet each side of it give good lighting, but the whole set-up should be carefully examined on the focusing screen before making an exposure. Another method is to place the tank close to a north window, with one floodlight on the opposite side.
Electronic flash or flash bulbs shining down from above the water surface can also be used.
The majority of fresh water fish may be photographed in a tank of the type described above. It is better to choose small specimens; a fish 6 inches long will make a better picture than one twice the size.
Any scenery included in the tank should be of the type usually associated with the fish to be photographed. When making records of a fish that spends most of its life at the bottom of the stream, for instance, the bottom, with characteristic weeds, should be shown in the picture. If the fish is a surface feeder, there is no need to show the floor of the tank. Since both the front and back of the tank are glass, extra scenery, and particularly the background, can be most conveniently built up outside and if they are thrown slightly out of focus it helps to give a feeling of depth to the picture.
Fish in Aquariums
The photography of the larger sea fish in public aquariums calls for special equipment and facilities not available to the ordinary photographer. A considerable amount of floodlighting is used and special precautions are taken to avoid reflections. Generally, there is an anti-reflection hood extending from the lens right up to the face of the glass, and part of the illumination may be provided by flash bulbs sealed into glass containers submerged with the fish.