Slit-scan cameras are used to shoot finish line photos due to the fact that recording a moving subject along a strip of film makes it impossible to miss any frames. Engineer and photographer James Guerin was interested in the distinctive look, so he went about building his own slit-scan film camera using an old Pentax SLR.
He ended up with the heavily modified camera seen above: a Pentax ME Super SLR that’s equipped with a special winding system that automatically moves film across a narrow slit as the photos are being exposed.
Yesterday we reported on how US Track and Field saw its first “photo finish” tie this past weekend in an Olympic qualifying race. If you thought the finish line photo looked strange, it’s not just you: it’s not an ordinary photo. Journalist Daniel Rutter has written up a great article on how finish line cameras work:
[...] most finish-line cameras aren’t super-high-speed movie cameras, but instead a kind of slit camera. A slit camera has a line-shaped lens, which exposes the film or electronic sensor line by line or column by column, not unlike the way a rolling shutter works. The critical difference, though, is that a slit camera can keep on going past the lens indefinitely. You can keep collecting image data, or keep spooling film past the slit, for as long as you have memory or film. The shutter never closes as long as the film or memory lasts, so it’s impossible to miss any action between the frames.
[...] imagine taking a flatbed scanner sensor and setting it up vertically, looking across a racetrack at the finish line. Start a “scan”, and it’ll authoritatively tell you when every body-part of every runner makes it to the finish, by simply showing that part of that person before any part of anyone else. The speed of the scan should be set to roughly match the speed of the runners, so they look generally the right shape, but any part of any runner that stays stationary relative to the scan rate – a foot on the ground, for instance – will seem long. Any part that’s moving forward relative to the scan rate – a hand or foot coming forward, for instance – will seem short. Even if you mess up the scan rate so everyone looks wide or narrow, whatever part of whatever runner shows up first in the scan is the first to cross the finish line.
Elastic athletes [How to Spot a Psychopath]
Image credit: Slitcam-Math by VanDerMouche
On Saturday night at the United States Olympic trials, sprinters Allyson Felix and Jeneba Tarmoh did something the sport had never seen before: tie on camera. Both runners crossed the finished line at exactly 11.068 seconds — see the photo above — and not even the high speed camera capturing 3,000 frames per second at the sideline could reveal a difference. Since this situation had never happened before, US Track and Field didn’t have any rule in place for how to deal with it. 24 hours later, they created a new rule: the athletes would be given the choice of breaking the tie with a coin toss or runoff, with runoff being the default if the athletes disagreed.
(via NYTimes via The Verge)