AF Assist Lamp

Vincent Bockaert, 123di.com

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. Notable higher end external flash systems feature their own focus assist lamps with far greater range.

The focus assist lamp on this Canon PowerShot S50 is located above the lens and beside the flash. It serves a double purpose. Firstly it fires a beam of patterned white light in low light situations which helps the auto focus system to get a lock. Secondly, when the flash and anti-red-eye are enabled it remains lit for as long as you half-press the shutter release to reduce the size of the subject's pupils and thus reduce the chance of red eye.

Hologram AF found on some Sony cameras works by projecting a crossed laser pattern onto the subject. This bright laser pattern helps the camera's contrast detect AF system to lock on to the subject. The system works well as long as the subject is large enough to be covered by several laser lines.

This article is written by Vincent Bockaert,
author of The 123 of digital imaging Interactive Learning Suite
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