Photo-Finish Technology

Photo-finish technology has spawned a handful of articles on how NASCAR determined the winner in a 0.001 second margin of victory at Kansas. I thought I understood the technology, but it turns out I hadn’t quite entirely gotten it.

I was slightly bothered by a post from NASCAR’s Mike Forde because I didn’t understand why it was an ‘image’ and not just a photo.

The Photo-Finish Camera

Cameras have been used to decide race finishes for quite some time. See Zack Albert’s lovely article for a story contrasting the Kansas finish with a back-in-the-day close finish. Original high-speed cameras, were one film, but today are digital.

NASCAR uses a camera made by Lynx. The critical thing Zack included in his article is that the camera is a line-scan photo-finish camera.

I didn’t find a picture on the Lynx page, but to the left is a line-scan camera made by Teledyne.

This kind of camera doesn’t take a full picture. That makes sense because if a camera is going to take a few thousand pictures per second, capturing a slice is all you need.

These cameras collect as little as a one-pixel-wide image. Basically, they capture only one stripe at a time. I’ve tried to illustrate this below. Each picture captures a set number of pixels.

The left-most photo is taken just as the #45’s splitter breaks the plane of the start-finish line. The next one catches next moment in time. And so on.

The Software Part of Photo-Finish Technology

Knowing how fast the photos are taken allows a software program to re-assemble these strips into a composite image, like the one shown below.

The camera technology is used anytime points are award, which means at the ends of stages and the ends of races.

There are a ton of articles about the finish, but this one question was bugging me. I think I have figured it out, but it you know I’m wrong, do let me know!

Please help me publish my next book!

The Physics of NASCAR is 15 years old. One component in getting a book deal is a healthy subscriber list. I promise not to send more than two emails per month and will never sell your information to anyone.


  1. This is similar to how an old school “photo finish” system worked. The camera at the S/F line had a narrow vertical slit and the film was pulled past the slit at a high rate of speed as the horse, dogs, cars, runners, etc passed by. The long strip of film was developed and there you had “The Finish”.


  2. Thanks Dick! That’s a great link between the filmic past and the digital present. Love learning something new. Thanks for reading!

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