Stroboscopic Lighting

Stroboscopic ("strobe") lighting for motion pictures has been available commercially for about 30 years. Typically these utilize xenon flashtubes which produce a good approximation of daylight (about 6000°K), and a relatively stable color temperature throughout life. Due to the fact that the flashtubes that are suitable for this application are either long slim sources or helical shapes, they can really only produce soft lighting. They can be color-corrected or adjusted using the same filter materials described for application to any of the normally utilized light sources and lighting instruments.

It is common practice to utilize continuous sources (such as tungsten) with strobes. Typical practice is to light 2 stops under the strobe with the tungsten lighting up to one stop over. The more tungsten lighting, the softer the image. The control equipment for these light sources permits an exposure duration of between '/ and Moaooo of a second. This permits stop motion with extraordinary sharpness of various phenomena, and delineates detail in realtime movement that is a blur in normal photography (even with very small shutter angles). The sharpness of results in slow-motion effects is unmatched by other techniques.

The strobes must be synchronized to the camera shutter. Usually the strobes are driven by the shutter pulse from the camera, and it is imperative that the units flash when the shutter is fully clear of the gate (otherwise a partially exposed frame will result). To check camera synchronization, the lens should be removed, and the cavity illuminated with the strobe with the camera turned on. The shutter should appear to be frozen in one position.

The control equipment for these strobes permits the addition of delay to the pulse in degree increments. The position of the shutter will either move forward or back ward in relationship to the gate until it is in the proper position. For reflex cameras the strobe fires twice for each frame, once to illuminate the subject and a second time to illuminate the viewfinder.

CAUTION: People with photosensitive epilepsy should be informed that strobe lighting will be in use.

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