Photo finish

A photo finish occurs in a sporting race, when two (or more) competitors cross the finishing line at near the same time. As the naked eye may not be able to discriminate between which of the competitors crossed the line first, a strip photo, a series of rapidly triggered photographs, or a video taken at the finish line may be used for a more accurate check. Nowadays, the photographs may be digital but usually involve special equipment. They may be triggered by a laser or photovoltaic means.

Types of photographs

There are two methods for creating a photo finish, the most common method uses a special slit camera, which produces a panoramic film strip. This camera uses a single vertical slit instead of a lens, and the film is advanced continously at a similar speed to the racers. This creates a 'virtual view' of the positions of each racer as they crossed the finish line, from the side without motion blur. Racers may appear compressed in this view based on the difference in the speed that the film is turning relative to their movement speed.

Related Topics:
Camera - Lens - Motion blur

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Slit-scan photography is similar, however the camera moves rather than the subject.

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The second method for creating this strip involves combining individual photographs. A high speed camera or a movie camera is used to take a continous series of partial frame photos at a fast rate, while leaving no blank space between the cells

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With all methods, time markings along the bottom of the photo can be used to find the exact crossing time of any racer, or simply used to compare their finishing positions along the strip.

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