Auto focus assist lamp
Digicams can be equipped with two kinds of autofocus. Active autofocus cameras emit an infrared beam which is reflected by the subject so the camera can focus on it.
Focus Assist Lamp -Lamp that assists in achieving focus where other cameras would fail. This is done by illuminating the object.
Focal Length - Distance from the lens to the film.
Focus Assist. Cameras with this send out a light, either normal or infra red to light up the subject to assist with the autofocus in low light or darkness.
Focus Assist - Some cameras employ a visible or invisible (infrared) lamp to illuminate the subject so the autofocus can work in low light or total darkness.
AUTOFOCUS ASSIST BEAM
Many cameras come equipped with an AF assist beam, which is a method of active autofocus that uses a visible or infrared beam to help the autofocus sensors detect the subject.
Focus Assist
When you try to take a picture in low light or virtually darkness, your camera, if it has this feature, emits regular or infrared light toward the subject, so the camera can see enough of the subject for the auto-focus to work correctly.
Focus Assist
Cameras can have a hard time focusing in dim light. For this reason some cameras will strobe the flash or fire a separate focus assist light. These lights briefly illuminate the scene, but work only at a short range.
Focus Assist
Visible or IR light system used by some cameras to help autofocus accurately under low light levels.
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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.
Magnified Focus Assist
To enable accurate manual focusing the E-P1 provides MF Assist Function and Magnification Display.
AF Assist - Auto Focus Assist - Refers to a feature built into either a camera or an accessory flash unit. It allows auto-focusing under dim lighting conditions.
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Normally, I would use the built-in model light from my strobe, but I've noticed that halogen bulbs, which are fine autofocus assist lights for subjects three feet away, ...
The primary disadvantage of all prism-based focus assist aids is that they can stop working and black out (become so dark as to be useless) when used with certain slow lenses, long telephotos, teleconverters or extension tubes, ...
Check the focus of the lens. You want to be sure that you can get focus. If it's a focus assist, check the assist function, and also its manual focus ability. The focus mechanism should move in and out with ease.
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(However, an autofocus assist beam of usually infrared light is required when there is not enough light to take passive measurements.) Passive autofocusing can be achieved by phase detection or contrast measurement.
Low-Light Focus - Focusing in low light is difficult for most cameras unless they have a focus assist light.
Creatively, I love the visual patina of shallow focus. Practically, viewfinder brightness makes a big difference in low light when you can’t use (or don’t want) the visual intrusion of focus assist.
 See also: Focus, Camera, Light, Digital, Photograph
  
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