High Speed Photography

No post production effects can duplicate the magic of film shot at high speed. In 35 mm we are still limited to about 360 FPS for the film stopping for each exposure. The rotary prism cameras go to 2500 FPS. In 16 mm, pin registered cameras go to 500 and rotary prism to 10,000. FPS but the image is not very good. The problem with rotary prism camera is that only a smaller image in the middle of the frame is sharp, the maximum shutter angle is 73 degrees and registration is poor.

We needed a shot of a tennis ball hit by a tennis racket at 2500 FPS. The odds of a player hitting a ball exactly in the right frame and place on the racket were not very high. We built a spinning racket rig to increase our odds of hitting the ball right.

At 2500 FPS with a 73-degree shutter you need a lot of light, about 8 stops more exposure than at 24 FPS with a 180-degree shutter, not including reciprocity failure. Sunlight is a great source. If shooting a smaller object plan to move everything with the sun's movement. If you need more than sun power, you can build a set of mirrors on 1" x 4' x 8' plywood that focus the light of 3 ea. 47" x 31" mirrors. Each single strength mirror will bend and focus light toward a 2 by 2-foot area at the foci of the mirrors. The mirrors can be tuned with pads glued to the back of the mirrors and adjusted with studs through the 1" plywood.

We used sunlight as fill and our concentrating mirror panel as 3/4 back rim key. This rig was heavy and not easy to move and focus. Today's faster films will help, pushing is acceptable because the image is not that sharp anyway. .

We used this rig to shoot tennis balls hitting the "sweet" spot of two tennis rackets spun at serving speed of 60 MPH. We dropped 30 tennis balls into the spinning rackets and got one or two direct hits per each take of 500-foot film take. Few of the balls hit the rackets at the right place and balls flew all over the set. Each ball was dropped from a chute with the label facing camera. A solenoid metered the balls one at a time out of a plastic tube. The rackets were attached to a bearing mandrel with a 3/4 HP motor turning the whole thing to give a racket speed of 50 MPH.

To split arrows we built a micrometer adjustable bow that could be re-adjusted each take. Care was taken to load each arrow exactly the same. The notch of the receiving arrows was removed and the back opened some to help the arrow hit the hole. We got about one hit out of four. The hits pealed the arrow back like a banana in all directions. Our actor had split arrows before, but we couldn't afford to shoot hundreds of takes to repeat his feat. We lit the shot with two separate 10 K Vegas with hot lenses to light the arrow, feathers, arrow head coming in and back ground to show.

To save print cost at the lab we always asked them to "print action only (described what the action is) plus and minus 10 feet".

16-mm tests can help find problems.

There are a few assistants who know high-speed cameras, but most of the time it is wise to get an assistant very well acquainted with these cameras.

Focusing the rotary prism camera is not easy. Using a sun burst (Siemen's Star) pattern focus chart will help.

The 35-mm cameras are very heavy and removable dovetails, heavy supports and heads are helpful.

Always consider double printing or video finish to get a higher apparent speed. Try to avoid the rotary prism camera if the 360-FPS camera will do the job, its image is so much better.

Be sure that you have the right 3-phase power, heavy cable and enough power to run these cameras. Not all 3-phase generators will run them.

A parallax video camera can be a little aid.

Everything that can be done to make each shot repeatable and controlled is worth the effort. To make cereal flow smoothly out of a box and not clump up we built a small motor driven conveyor belt to deliver the flakes smoothly out of the box. The belt was a strip of film driven by a DC gear motor with film sprockets. The cereal box covered the conveyor. The box and conveyor well supported.

When shooting you can save film by timing "action" not by the assistant calling "speed", but by the person triggering the event when he hears the camera hits speed by sound. The assistant can then shut the camera off and apply a brake it if possible to stop it faster.

© Copyright 1999-2004 Ron Dexter. All Rights Reserved.