The cameras are fitted with fixed-focus lenses and wide angle adapters and are permanently mounted in custom housings. Wide angle adapters are necessary because the cameras on the submersible toe in toward each other so that their fields of view intersect approximately 2 m in front of the submersible. Each camera's field of view must be as wide as possible because images outside the volume of water viewed by both cameras are recorded on only one videotape, and are useless for 3-D analysis. The camera housings are rigidly mounted on either side of the submersible because the positions of the cameras relative to each other must remain constant to track an object accurately. A control box remotely powers both cameras and electrically controls the irises.
Video recording is controlled from two VCRs inside the submersible.
Sequences on the two videotapes must be synchronized for subsequent identification of identical frames. When the original tapes are dubbed onto work tapes, the auditory time code is transformed into a visual code in minutes, seconds, and frame numbers at 30 fps, that appears on every frame. The greatest advantage of the time code over periodic synchronizing signals, such as a strobe flash or tone, is that the continuous visible code allows the user to be sure that identical sequences of frames on multiple videotapes are selected for digitizing. We use Super-VHS or Hi8 videocassette recorders because of their high video resolution. For recording from the Johnson Sea-Link , where space was limited, we used 2 portable VCRs.