Digital SLR Camera Basics


flash compensation

The act of adjusting flash output from the value selected by the flash unit and camera. For example, flash output can be increased to light the subject more brightly, or decreased to make lighting less harsh.

flash control

A system for adjusting flash output based on the amount of light reflected from the subject.

flash-ready indicator

An indicator that shows if a flash unit is charged and ready for use.


A unit used to measure the brightness of the image projected from the lens onto the image sensor.

focal length

The distance from the middle of a lens to the image sensor.

focal plane mark

A mark on the camera body indicating the position of the image sensor. In digital SLR cameras, the distance to the subject is measured from the focal plane mark.


The point at which light rays converge; the act of adjusting an optical system so that the light from the subject converges at the focal plane. Subjects that are in focus are sharply detailed, while subjects that are out of focus appear blurred.

focus lock

The act of fixing (locking) focus at the distance to a selected subject; while focus is locked, the photographer can change the composition without changing focus. This is effective if the subject in question will not be in a focus point in the final composition.

focus point

An indicator showing a point in the frame that the camera can use for autofocus.

focusing screen

An element between the mirror and pentaprism or pentamirror in a single-lens reflex camera. The mirror reflects the image from the lens upward onto the screen. The areas of the image that are in focus are sharply defined on the screen, while the areas that are out of focus appear blurred. The photographer views the image passing through the screen in the viewfinder window.

front-curtain sync

A flash mode in which the flash fires as the shutter opens. This mode is used in most flash photography.

See also: rear-curtain sync