AF Assist Lamp: Camera System: Glossary: Learn: Digital Photo...

Some manufacturers fit their cameras with a lamp (normally located beside or above the lens barrel) which illuminates the subject you are focusing on when shooting in low light conditions. This lamp assists the camera's focusing system where other cameras autofocus will likely have failed. These lamps usually only work over a relatively short range, up to about 4 meters. Some lamps use infrared light instead of visible light which is better for "candid" shots where you don't want to startle the subject.

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