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.
Method of capture
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 20s 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.
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 it 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 along the length of the body 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 but still preserving the order of finishers.
Improvements were developed, including that made in 1948 by Australian Bertram Pearl whose system incorporated a mirror and neon-pulse time signature in the winning-post which would provide a precisely aligned image in which both sides of the horses could be viewed, and on which the neon left a set of stripes at 100th/sec intervals for accurate timing. If the reflected image of the horses aligned vertically exactly with the foreground image, it was proof that the camera was not viewing the finish-line at an angle (and therefore incorrectly recording the horses' relative positions). Pearl's partner was his friend, society portraitist Athol Shmith. Shmith’s contribution was to formulate means to speed the processing of the strip of negative down to 55 seconds and then to a rapid 35 seconds. These times rivalled even the ‘instant’ one-minute picture processing by Edwin Land’s Model 95 which became available at that time.
Digital cameras use a 1-dimensional array sensor to take 1-pixel-wide sequential images of the finish line. Since only a single line of the CCD is read out at a time, the frame rates can be very high (up to 10,000 frames per second). Unlike a film based photo finish, there is no delay from developing the film, and the photo finish is available immediately. They may be triggered by a laser or photovoltaic means.
Another method for creating this strip involves combining individual photographs. A high speed camera or a movie camera is used to take a continuous series of partial frame photos at a fast rate, while leaving no blank space between the cells.
In athletics, races have to be timed accurately to hundredths (or even thousandths) of a second. A battery of electronic devices are installed in high-profile events (such as the Olympic Games) to ensure that accurate timings are given swiftly both to the spectators and to the officials. The photo finish has been used in the Olympics since as early as 1912, when the Stockholm Olympics used a camera system in the men's 1500 metres race.
At the finish line, photocells and digital cameras are used to establish the placings. Sometimes, in a race as fast as the 100 m sprint, all eight athletes can be separated by less than half a second. It is not uncommon for two athletes to have exactly the same time recorded without there being a deadheat.
The 2008 Summer Olympics saw the introduction of some of the fastest timekeeping equipment yet, with cameras that take photographs 3,000 times a second (compared to 1996, which were 1,000 times per second).
The 2012 Summer Olympics had a photo finish during a triathlon event in which Nicola Spirig of Switzerland and Lisa Nordén of Sweden finished the race at nearly the same time, but with Spirig ranked first. The Swedish Olympic Committee appealed the ranking. They claimed that the athletes should be ranked as joint winners because it was not clear that Spirig was ahead of Nordén. The camera on the far side of the track may have given additional evidence, but it was malfunctioning. The appeal was rejected and Spirig was declared the winner. This is the first time an Olympic triathlon result was decided on a photo finish.
- On July 15, 1995, Butch Miller beat Mike Skinner by .001 seconds to win the Total Petroleum 200. It is the closest finish in NASCAR history.
- On June 14, 2008, Erik Darnell beat Johnny Benson by .005 seconds to win the Cool City Customs 200.
- On October 30, 2010, Kyle Busch beat Aric Almirola by .002 seconds to win the Mountain Dew 250, the second closest winning margin in history.
Two races have tied for closest margin for a photo finish in the Sprint Cup Series:
- The 2003 Carolina Dodge Dealers 400 at Darlington Raceway, where Ricky Craven won over Kurt Busch by 0.002 seconds
- The 2011 Aaron's 499 at Talladega Superspeedway, where drafting help from Dale Earnhardt, Jr. allowed Jimmie Johnson to win the race by 0.002 seconds over Clint Bowyer
- Although not officially in a points-race, in 2001, Mike Skinner won a Gatorade Duel at Daytona by inches over Dale Earnhardt, Jr.
In horse racing, a factor known as a dead heat can occur, when two—or possibly more—horses cross the finish line at exactly the same time. Photo finishes determine accurately when the horses hit the finish line. This developed in the late 1930s, by the end of which strip cameras were used for photo finishes; prior to this point high speed motion picture cameras were used, but did not provide sufficient temporal resolution. Stewards at the racetrack usually put up PHOTO status on the races during these photo finishes; the status of objection or inquiry can also trigger if other horses or jockeys somehow interfered in the horse rankings and can factor in dead heats. The most notable dead heat was in the 1989 Hambletonian Stakes, with both Park Avenue Joe and Probe finishing in a dead heat. A photo finish decided the winner of the 2005 running of the Japan Cup, which was given to Alkaseed, narrowly defeating Heart's Cry. And in 2011 with new digital technology recording vision at 10,000 frames per second, Dunaden was declared a winner over Red Cadeaux in the $6 million Melbourne Cup.
- "Company Registered To Handle Camera Eye.". The Argus (Melbourne, Vic. : 1848 - 1956) (Melbourne, Vic.: National Library of Australia). 2 August 1946. p. 11. Retrieved 12 February 2013.
- "SPEED RECORDS WITH CAMERA EYE.". Advocate (Burnie, Tas. : 1890 - 1954) (Burnie, Tas.: National Library of Australia). 17 July 1945. p. 3. Retrieved 12 February 2013.
- (In Swedish) Article in technical magazine Ny Teknik. Also with a picture of the finish line at the stadium
- Olympic Timekeeping More Accurate Than Ever Discovery Channel News . Retrieved 22 August 2008.
- Court of Arbitration for Sport (CAS) Decision. Retrieved 13 August 2012.
- "Strip Tease: An introduction to the strip camera, how Tom Dahlin made his, and how you can too.", Tom Dahlin, SportsShooter, 2008-08-18