Q How does the Zone System apply to the use of electronic flash

A: In general, the correct exposure with electronic-flash units is calculated by carefully measuring the camera-to-subject distance with the range-finder on the lens and using this to select the proper f/stop with the exposure dial on the flash. You must use the shutter speed that is synchronized with your flash, usually 1/60 or 1/125 of a second (check your owner's manual). As noted in an earlier chapter, with modern electronic-flash units, the exposure is determined by a thyristor circuit that controls the output of the flash. Dedicated flash units automatically adjust both the f/stop and shutter speed of the camera.

The Zone System allows you to accurately measure the contrast of your subject. If you determine that the contrast is too great, you have two choices: You can base your exposure on the shadow areas and reduce the contrast of your negative by decreasing the negative's development time, or you can expose for the highlights and add more light to the shadow areas with fill-flash. This usually involves setting the flash to 1/2, 1/4, or 1/8 power depending on how much fill you need. The instructions provided with your flash will explain how this is done. The second procedure is especially useful in back-lighting situations with both black-and-white and color films.

In a photographic lighting studio where you are essentially starting with a "blank canvas," the art of previsualizing becomes an extremely important part of the overall creative process. Ordinarily studio photographers use powerful electronic strobe units with power packs to light their subjects. The lighting composition is done with built-in modeling lights that are much less bright than the flash itself. Because the bursts of light from the flash heads are extremely short, special flash meters are required to measure the incident light and provide an exposure. Since the shutter speed is fixed and synchronized with strobe, flash meters provide their readings as an aperture number. The brighter the light the smaller the aperture. It is very common for studio photographers to use Polaroid film to help them previsualize their lighting and to help calculate the exposure.

Contemporary spot-flash meters now allow you to take reflected strobe readings of the key areas of your subject. This makes the application of Zone System concepts in the studio a straightforward process. By carefully measuring the contrast of your subject you can previsualize your image and determine how much extra light to add with fill-cards or lights. Once the contrast has been balanced and adjusted your film is usually given Normal Development.

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