A Viewfinder Darkly

Photography tips and tutorials

How the Photo Finish System Works

April 21 2014

by Philip Northeast

Digital photo finish cameras do more than help the judges decide who won a race.

Judges at tracks around the world use special photo finish systems as they decide the winner of a race. The photo finish camera and software also helps judges to accurately tell how fast the competitors went and the winning margins. Despite all the electronic wizardry the system still relies on basic photography techniques.

The system is can be used for people, horses, or greyhounds. A visit to a local track using the FinishLynx system provided insights into the specialised parts of the system, as well as those familiar to photographers.

Not an Ordinary Photo

The image produced by the photo finish system may seem like a normal panoramic picture it is instead a composite image built from a large number of very narrow images. The photo finish camera takes a narrow vertical image of the track along the finish line and the width of the image is the width of the finish line.

Photo finish image with the moveable cursor on the nose of the winner


Photo finish image with the moveable cursor on the nose of the winner

A normal photo is a moment in time, but the photo finish image is many moments in time. These images are   combined from right to left to show what is happening at one point, and when it happens. Try viewing an object through a narrow vertical slit as you move the object past the slit. Even though you are only seeing a tiny part of the object at any one moment, eventually you see the whole object as it passes through the narrow field of view of the slit.

The camera and software add new sections to the image to the left of the starting section, so as something moves through the finish line the system builds a complete picture resembling the moving object or animal.

Shutter Speed

The rate of capture is a factor when photographing moving objects. In normal photography this is how long the shutter is open. But the high speed digital photo finish system uses a very short capture time for an image. Instead the number of frames per second is set to suit the speed of the racers, for greyhound racing, this is about 1600 frames per second. When somebody runs, their legs move at a different rate to their body and sometimes the result is weird shapes for legs and arms in  a photo finish picture. The system is set to capture the bodies of the animals in the right proportion rather than the legs of a competitor.

The normal broadcast television system covering most race meetings cannot guarantee to capture  a frame just as a competitor reaches the finish line. This is due to television’s relatively slow frame rate, in the order of 50 per second, compared to 1600 frames per second for the greyhound racing photo finish system.

Interchangeable Lenses

While much of the camera system is high technology, the optical system is still basic. The Finish Lynx camera uses standard DSLR lenses, in this case the camera uses Nikon telephoto lenses, although Finish Lynx do a make a version for c-mount lenses.

The racing complex for this article combines three codes of racing, Thoroughbreds, Harness racing and Greyhounds, the result is four tracks.

The thoroughbreds use two outside turf tracks, there is one crushed granite track for harness racing, and in the very inside is the sand greyhound track. The combined venue places additional demands on the system, particularly as the smallest and fastest animals run in the centre track and they are furthest away from the camera in the judge’s tower.

Four tracks

Four tracks for different racing codes in the one complex

 

To cater for the variety of distances to each track there is a choice of a 300mm prime lens for the Greyhounds and a 70-200mm zoom for the other three tracks. The lenses have large f2.8 maximum aperture for two reasons. Firstly, at night under lights they allow enough light for a reasonable exposure. Secondly, the large apertures provide brighter images for the critical manual focusing due to the shallow depth of field resulting from the long focal lengths of the lenses.

The head of the photo finish section at the complex, Michael Foster, says focusing is the most critical aspect of setting up the system for a race meeting. Any out of focus blurring in the image makes it difficult to pinpoint the edge of the nose.

There is a hand operated reflex mirror in the Finish Lynx camera for manual focusing using the optical eyepiece.  An option is the focus assist feature in the software that analyses the image and presents the operator with a focus quality number, the higher the number the sharper the focus. The operator still has to manually adjust the lens to achieve the best focus.

Composition

The operator uses the optical viewfinder with a manual operated movable mirror to look through the lens, the same as DSLRs,  to compose the images. It is critical that the camera is exactly lined up on the finish line because any misalignment could alter the result of the race. There are marks inside the viewfinder to assist in lining up the camera in the middle of the yellow line on the bottom of the mirror tower.  The other important aspect of the composition is ensuring that all the track and the entrant’s reflection in the mirror are in the photos.

The finish line indicated by the yellow line on the mirror tower

The finish line indicated by the yellow line on the mirror tower

Exposure

There are no automatic scene modes. Setting the exposure setting is a matter bases on taking a test shot and adjusting the aperture ring on the lens. Through a race meeting, the operator is constantly monitoring the exposure as the light changes.

Each camera has to have the white balance set individually due to differences in the camera, although they seem to cope with transition from daylight to floodlights once set properly.

 

Digital Not Film

As is the case in most 21st century photography the Finish Lynx system is digital instead of the original film systems.   The photo finish camera connects directly to the operator’s computer via an ethernet cable and the image is ready as soon as the last runner crosses the line. Digital systems have another advantage, it is easy to convert the image to a video signal for immediate transmission to the television broadcaster.

Another digital advantage is the ready calculation of race times and margins. When the doors on the starting barrier open, sensors send a signal to the judge’s tower to start the clock in the Finish Lynx system. This allows the computer to calculate the race time for each runner.

Each sport has a specific point on the body, or machine, in their rules that is used to measure when the competitor has crossed the finish line. For example in horse and dog racing it is the nose while in cycle racing it is the front tyre.

Once the horse or greyhound race is over the photo finish operator displays the image a  computer running a software application compatible with the photo finish camera. The operator places the movable vertical line cursor on the edge of  the animal’s nose and this corresponds to one of the thousands of timestamped images that make up the composite photo finish picture.

Entering the race number using the keyboard associates the competitor with this position and calculates the competitor’s race time.  The software uses the race times to display time differences between competitors and can also estimate the distances between competitors at the finish line.

 

The image in the trackside mirror shows two views of the finish

The image in the trackside mirror shows two views of the finish

Final Word

Although there is considerable computer assistance in creating the composite photo finish image and interpreting the results, the essentials of photography are still valid. This illustrates that even in the age of highly automated digital photography an understanding of light and optics is fundamental for photography.

 

 

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