the actual duration of the flash is over in less than a
1/2000 second ( many flashes are much faster up to 1/10000 second
) and with focal plane shutters this has to be synchronized
so that the two blinds of the shutter are completely open. One
blind needs to have completed its movement across the focal
plane, while the other has not yet begun.
Most SLR focal
plane shutter cameras have shutters that are synchronized
at 1/60 sec. This is often marked on the shutter setting with
an X or the setting are in a different colour. If a photographer
uses a shutter speed faster than this synchronized speed the
image will appear as a thin slit, the faster the shutter speed,
the smaller image.
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