This past weekend millions of people tuned in to watch the “most exciting two minutes in sports,” the 139th running of the Kentucky Derby. The Derby is the longest consecutively run horse race event in America. Although this year’s winner, Orb, won by two and a half lengths ahead of his competitors, the winner has been determined by a neck or less on 13 occasions since the Derby was first run in 1875.

Before photography was used, a placing judge who stood at the finish line had the final say in which horse had won. However, many people, including famous photographer Eadward Muybridge, were of the opinion that horse racing and other sports depended on new technology for accurate results. In a letter to the editor written to Nature in May of 1882, Muybridge stated “I venture to predict, in the near future that no race of any importance will be undertaken without the assistance of photography to determine the winner of what might otherwise be a so-called ‘dead-heat’.” (Scientific American is part of Nature Publishing Group.) In 1878 Muybridge had created the means to take photos of a horse in motion by placing a thin wire across a point of a horse track, which attached to a series of mounted cameras. When the wire was tripped, the cameras would go off, taking a series of simultaneous images. Scientific American featured some of these on the cover of their October 19th, 1878 issue.

The first documented use of a photo finish at a horse race was in 1881. The photo was taken by official racing association photographer Ernest Marks at a track in Plainfield, N.J. Cameras continued to be used in the early 20th century, along with new motion picture technology. But, because of their horizontal shutters, a horse on the inside of the track would be captured on the film whereas a horse on the outside would still be in motion, often creating images that would deem the outside horse ahead of the pack. As betting on horses became more and more prominent in the 1930s and ‘40s, it was clear that something had to be done to produce accurate race results in an industry that already had all the corruption it needed.

In 1937 Lorenzo del Riccio developed what is called a “strip camera” that utilized a single vertical slit rather than the traditional horizontal shutter. A sound and color engineer for Paramount Studios in California, del Riccio was able to perfect the device so that the image it produced showed different points in time at a fixed location instead of showing different locations at a fixed point in time. His invention, first used at a horse race at Bing Crosby’s Del Mar Turf Club in California, was later featured in the January 1941 issue of Scientific American.

The camera itself would be mounted at the top of the stands, along with a complete darkroom for quick developing. The slit in the camera was focused solely on the finish line. A telephoto lens with a five-and-a-half-inch focal length and f2 aperture captured the entire width of the track on film, which moved past the open slit at about the same relative speed as the horses. This allowed the horses to be in focus whereas the background would be a white blur. On average, it took about 48 seconds for the film to be developed. Del Riccio recognized that races taking place in the late afternoon would cause lighting problems, as shadows and low light would make for difficult to read photos. To rectify this, he engineered “Photo Chart” equipment, consisting of 1000-watt, water-cooled mercury lamps, first installed at Hollywood Park racetrack.

The lamps were placed in housing near the finish line and helped to illuminate the finish line tape. Ballast transformers for power and water-control equipment used to cool the lamps were kept in the same location. Atop the stands, a 24-inch Mole-Richardson “sunspot” with a triple-mercury lamp, placed at a 20-degree angle to the finish line, would be directed into a narrow-beam at the tape in the direction of the oncoming horses. With adequate light projecting on the horses as they crossed the finish line, the accuracy of judging a winner greatly improved. According to Scientific American, del Riccio’s work helped take all but one variable out of horse racing: “the selection of the horse itself!”

Although digital cameras are now used for photo finishes, the technology developed by del Riccio was instrumental in reassuring gamblers they were betting on fair outcomes, and helped bring horse racing maintain its popularity in American culture. There are still two of of three Triple Crown races left to run this season (the Preakness Stakes and the Belmont Stakes), so be sure to keep your eyes on the finish line to see if Orb has what it takes to win it all!