flash, pre- (preflash) A low-output flash fired before the main flash to measure the distance to
the subject and to calculate how the main flash should be fired to create a correct exposure.flash, slave A flash unit that fires in response to the firing of a master flash unit.
flash, slow-sync mode To better expose in a night shot the background beyond the range of a
flash unit, slow-sync holds the shutter open long enough to capture more of the background before
firing the flash to expose the main subject in the foreground.flash, stroboscopic A series of individual flashes fired quickly while the shutter is open, captur-
ing multiple exposures on a single frame. Stroboscopic flash is effective for capturing movement
against a dark background.flash, x-sync An electrical setting that makes the flash fire when the shutter is fully open. In SLR
cameras equipped with a focal-plane shutter, the x-sync speed is the fastest shutter speed at which the
first and second shutters are fully open.flash exposure compensation A flash unit adjustment that changes the amount of light the
flash provides to fine-tune the balance between foreground and background exposure.flash memory card A card containing chips that store images using microchips instead of
magnetic media.flash synchronization Firing of the flash as the shutter curtains open and close so that the
scene will be evenly lit.focal length The distance, in millimeters, from the optical center of the lens to the image sensor
when the lens is focused on infinity. Also defined as the distance along the optical axis from the lens
to the focal point. The inverse of a lens’s focal length is called its power. Long focal lengths work like
telescopes to enlarge an image; short focal lengths produce wide-angle views.focal point The point on the optical axis where light rays form a sharp image of a subject.
focusing Adjusting a camera’s lens system to bring the subject into sharp view.
formatting Completely erasing and resetting a camera’s memory card so that it can accept new
photos.G–H
gamma A mathematical curve created by the combined contrast and brightness of an image,
which affects the balance of the middle tones. Moving the curve in one direction makes the image
darker and decreases the contrast. Moving the curve in the other direction makes the image lighter
and increases the contrast. The blacks and whites of an image are not altered by adjusting the
gamma.gamma correction Changing the brightness, contrast, or color balance by assigning new val-
ues to the gray or color tones. Gamma correction can be either linear or nonlinear. Linear changes
affect all tones, non-linear changes affect limited areas tone by tone, such as highlights, shadows,
or mid-tones.(^206206) GLOSSARY