PHOTO FINISH AND HOW IT WORKS
The “Photo Finish” is one of those operations, like many other present day occurrances [occurences] which are just taken for granted, and Mr. Roberts, the H.B. Representative of Photo Finish Australia Ltd., and the man who operates the photo finish cameras throughout Hawke’s Bay, probably overestimated the position when he expressed the opinion that not more than one per cent of the racing public know just what happens. Here in pictures and words, and with the very generous help, and patience, of Mr Alan Roberts, Photo News endeavours to explain how it all works.
Less than 1/200th of a second separates the 1st and 2nd placing in this race, but the camera clearly shows the winner as being No. 1. As the captions on the photo show, the vertical white lines represent 1/100th of a second, and it is possible to separate horses when there is only a difference of 1/800th of a second between them. Consequently there are not many dead-heats recorded, perhaps only two or three a year.
All regular racegoers will have seen the tall thin mirror at the finishing post and on the inside of the track. This mirror is 8 ft. by 6 ins. and is 180 feet from the camera lens, the cameras usually being installed in the stands dead opposite the finishing line. These cameras are so set up that only 1½ ins. (width) of the mirror is “seen” by the lenses. On the photo reproduced opposite, this represents an area of approximately 1/3 of an inch. More accurately, the actual camera width in the camera is .006 of an inch. Thus at no time is a complete horse photographed, the picture is actually a built up image formed as the horses pass the “survey line” or finishing line, only 1½ inches of the horse being exposed to the camera any one one time.
The film in the camera is also moving across the .006 inch aperture for a total exposure of .7 of a second on any one print or enough time for the equal of 70 lines (shown on the picture opposite) to pass in front of the camera. This explains why the horses legs don’t always appear to be in the positions they ought to be. The lapse of time between the front and back pair of hooves passing the camera aperture is sufficient for the latter to have changed position. (All very confusing, but that is what happens.)
This continuous exposure also accounts for the “flow lines” which are caused by the film moving across the slit in the camera and picking up light and shade on the grass.
The spinner is a circular band (with the information written on it) situated at the bottom of the mirror. The speed in which it spins is synchronised with the film speed.
The camera man’s view of the finishing line. Note the 8′ x 6″ mirror in centre background, and remember only 1½” of that 6″ width is “seen” by the cameras. The lower camera is the “master” one and the top camera is used as a check and also for photographing horses that run wide.
The cameras are powered by electric motors and are set in motion when the horses are about 1½ chains away from the finishing post. Mr. Roberts has just started them up, and by the time the first horse reaches the post, the cameras will be running at their correct speed.