by Andrew Davidhazy
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High-Speed is a gallery of high-speed
photography by Andrew Davidhazy,
a professor at the Rochester Institute of Technology. Andrew says that high-speed photography "actually implies two things. One is that one is setting out to make photographs of fast moving events and the other is that one wishes to make sharp and blur free photographs of these subjects. A conventional subject for truly high speed photography is a free-flying .22 caliber bullet and its impact on various objects." What you see here is the impact of a bullet on various objects, but the effect is hardly conventional.
Here is an explanation of the process:
High speed photography actually implies two things. One is that one is setting out to make photographs of fast moving events and the other is that one wishes to make sharp and blur free photographs of these subjects. A conventional subject for truly high speed photography is a free-flying .22 caliber bullet and its impact on various objects.
If one attempts to make a photograph of such an event it quickly becomes obvious that the major problems one will have to solve are the achievement of exposures times that essentially prevent the subject from appearing blurred in the final photograph and the synchronization of the camera exposure with the bullet being at a particular time and location in space.
Deciding on an exposure time necessary to achieve blur free photographs is dependent on the amount of blur one can tolerate before calling the photo unsharp and the rate of travel of the subject. In the case of a .22 bullet moving at about 1,000 feet or 12,000 inches per second and assuming that we desired to limit movement of that bullet to less than 1/100 of an inch, the exposure time required would be 1/100 inch divided by the rate of motion of the bullet or 12,000 inches per second giving us a desired exposure time of about 1/1,000,000 second.
A normal camera does not meet this requirement. To achieve truly short exposure times an auxiliary exposing device is required. An EG&G 549-11 "Microflash" electronic flash with a .5 microsecond duration will amply meet the requirements but it needs to be triggered at the right instant in time. At the time the subject is changing its appearance due to the impact of the supersonic bullet!
Synchronizers that enable the firing of the Microflash at the right instant in time can be quite sophisticated and expensive or simple and cheap. My students and I prefer the latter and simply couple a standard cassette tape recorder to a high sensitivity electronic switch (an SCR) and this, in turn, fires the electronic flash when a sound, or the shock wave of a supersonic bullet, is picked up by the microphone. The position of the microphone is adjusted to trigger the flash when the bullet has just passed through the subject of interest.
The photographs are made under darkened conditions because the camera shutter needs to be opened awaiting the burst of light from the flash. Since this would cause pre-exposure to ambient light, this is extinguished, and the environment is essentially made part of the camera system.