Photo finish

A photo finish occurs in a sporting race when multiple competitors cross the finishing line at nearly the same time. As the naked eye may not be able to discriminate between which of the competitors crossed the line first, a photo or video taken at the finish line may be used for a more accurate check.

Finish line photos are still used in nearly every modern racing sport. Although some sports use electronic equipment to track the racers during a race, a photo is considered the most important evidence in selecting the winner. They are especially important during close races, but they are also used to assign official times to each competitor during any race.

Photo-finish cameras were developed during the 1940s and 1950s as a means of regulating the racing industry and to reduce cheating. Betting on races became increasingly popular during the middle decades of the twentieth century. Authorities were therefore concerned to improve the probity of racing which was widely regarded as corrupt.

Typically photo-finish cameras use strip photography, in which a camera is aimed at the finish line from an elevated position in a tower. It captures only the sequence of events on that line in the vertical dimension. Every part of each racer's body is shown as it appeared the moment it crossed the line; anything stationary is represented as a horizontal streak. The horizontal position represents time, and time markings along the bottom of the photo can be used to find the exact crossing time of any racer. The high angle allows judges to see the position of every racer in relation to the others.

In a conventional photograph, the image shows a variety of locations at a fixed moment in time; strip photography swaps the time and space dimensions, showing a variety of times at a fixed location.

The final image often shows a solid white background, which is a continuous scan of the painted finish line. Racers may appear distorted based on the movement of their limbs and heads as they cross the line; limbs are elongated where they remain static or move backwards in relation to the slit-shutter, or truncated if they move faster than the film moving past the slit.

Historically, in the United States motion picture cameras had been used 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 horses or dogs reached the finish line. This record 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.

...
Wikipedia