positioned at the finish line and initially applied to horse racing. The camera’s shutter which captured 136 images each second was triggered as a horse broke a thin thread on the race track. All too often, the single-exposure photo-finish camera failed to capture the decisive, first-place finish-line moment. These cameras only were used for first-place finishes, and provided no help in determining any of the other race placings. The oldest single-exposure race-track photo-finish images discovered so far were made by John Charles Hemment in 1890. Historically, motion picture cameras had been used in the United States since the 1920s for recording race-meets but were unsuitable for photo-finish photography as the frame rate was too infrequent to catch the critical instant when horses or dogs reached the finish line. This was achieved by using a special slit camera. Lorenzo Del Riccio, a Paramount Pictures motion picture engineer improved the circular flow camera, a device which had been invented in the 1930s especially for the purpose of photographing moving objects. The first racing club to make use of Del Riccio's 'Photo-Chart' camera for photo finishes was the Del Mar Turf Club in California at its inaugural meeting in 1937. Unlike conventional cameras the circular flow camera used a single vertical slit instead of a shutter; a strip of film moved horizontally across the fine vertical opening located in the focal plane. This limited the field of vision to no more than a few inches, the restricted field being aligned with the vertical line on the winning post on which the lens was focused. The strip film moved across the slit in the opposite direction to the race and at substantially the same speed as the rate of movement of the image of the horses as each passed the finishing line. This kept the image of the horses more or less stationary with respect to the film. As soon as the first horse started to pass over the line, the camera began to record its image on the moving film from the nose backwards, progressively along the length of the body, with the arrival of every horse at the finishing post in succession. This produced a strip photographic record of the horses as they passed the vertical plane (winning post). Film was advanced continuously at a pace equivalent to the average speed of a racing horse, resulting in distortions of length (slower-moving horses