Hidden Flaws Bared by High Speed Movies (Dec, 1938)
Making a high-speed movie has gotten a lot easier and cheaper in the digital age. There are some really cool ones on You Tube.
Hidden Flaws Bared by High Speed Movies
THE “movie doctor” is not human. It is a machine that in its own line can do more than any human being. It specializes in diagnoses, because with its keen, rapid-seeing eye, it can peer at machines, watch the way they work, and point out just what is the matter with them.
This movie doctor is an exceedingly high-speed motion-picture camera, now used in conjunction with a precision clock. It is really a sort of time microscope. In it is used the ordinary sixteen-millimeter moving-picture film, which takes pictures of the object under examination and at the same time records the time of each frame. While the ordinary motion-picture camera is designed to run at a rate of around sixteen pictures per second, this high-speed camera
can run at a speed of 2,500 pictures per second, and a specially constructed camera can run as many as 4,000 pictures per second. When the pictures taken at high speed are projected at the normal rate of sixteen pictures per second, the motion appears to be slowed down more than 150 times.
The time of each frame is photographed on one side of the film. The clock used with this camera is a precision timepiece by which it is possible to read the time to a little closer than 1/1000 of a second. This result is obtained by means of two dials, one with sixty divisions rotating once per minute, the other with 500 divisions rotating once per second. With this combination camera and clock, not only panchromatic and super-panchromatic film can be used but also color film. This last is particularly useful for photographing flames and chemical processes, as by its use gases emitted may be identified by their characteristic colors. Photographs can be made in sunlight or by the light of photo-flood or spot lamps, and bright, self-luminous objects can be photographed without the use of additional lighting.
One of the first uses for the high-speed photographic timer was in sports events, where it proved its usefulness in revealing the exact time of runners. In this work, it is usually not necessary to have the exceedingly high-speed camera. While the machine used operates on the same principle, together with the time device, for horse races, for instance, it is gauged to take from 128 to 150 pictures per second, which is sufficient speed for photographing the action. These cameras at this speed have been found to be excellent for determining the results in closely contested races.
The value of this mechanical diagnostician, at its very high speeds, goes far beyond the realm of sports, and has made itself felt in connection with some of the most common of our modern inventions. The diagnoses of this high-speed camera are being sought in industry for analysis of manufacturing processes and the solution of problems concerning the design and performance of machinery.
The smoothness of operation of an automobile may be the result of examinations conducted in the factory by means of high-speed photography, for the automobile companies use this camera to study vibrations and the rates of combustion of fuels in motors.
In aeronautics, too, this device is used to investigate air flow around structures and as a guide in the design and performance of propellers.
The extent to which the high-speed camera is finding application to problems concerning telephone apparatus is indicated by the fact that about two thousand films have been made of various telephone operations. One group of frames taken by high-speed photography shows the action of the impulse wheel, pawl and snubbing spring in a telephone dial. One high-speed photograph disclosed the cause of a peculiar acoustical effect. This series of frames showing the action of the clapper striking one gong of an experimental ringer, revealed more strokes of the clapper per cycle than were desired.
In testing firearms, probably no other mechanism can so accurately follow and record shots and the speed of bullets; consequently the high-speed camera is frequently used in ballistic studies.
This camera, together with lighting equipment and the timing apparatus, can be moved about easily, so that it can be used in a wide variety of studies, and its use is growing in demand in industry. By the use of high-speed photography with a precision timer, not only can mechanical movements too rapid to be seen by the eye be analyzed, but these photographic records give definite space-time relationships between moving parts of the machinery. Such photographs may reveal why machines do not function exactly as designed, when parts bounce, bend or break, and where moving parts create currents in liquids or gases. The device is especially useful in studies of transient movements such as contact chatter.
This movie doctor examined a severe case of chattering in part of the mechanism of a motion-picture projector, and the resulting photograph revealed the cause of the trouble.
Sewing-machine companies and shoe companies have found uses for high-speed photography, and companies using highspeed machinery for manufacture of fragile materials such as paper, thread, and transparent cellulose, are dependent upon this device, for when there is a breakdown or any failure in such machinery, often, after the failure, it is impossible to discover just where the fault lay. A photograph of the machinery by means of a high-speed camera, even at a time when everything is operating smoothly, may often reveal some hidden flaw which must be corrected in order to avoid future failures.
One of the most recent applications of high-speed photography is in the field of biology and medicine, where it is used to study nervous and muscular reactions under controlled conditions.