IF (Internal Focusing) System
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INTERNAL FOCUSING - Lens in which internal lens groups shift during focusing so that the external length of the lens does not change.
Internal Focusing. A conventional double helicoid focusing system requires that all lens groups be moved by the lens barrel to either the front or rear during focusing.
-IF (Internal Focusing) - system in which only the internal lens group shifts during focusing.
Internal focusing can confuse people, for instance, the Nikon 18-200mm lens reduces its effective focal length when focused closely at 200mm.
Internal Focusing - Types of lens that have internal components that can be adjusted in order to focus a shot, rather than depending on adjusting the lens barrel.
Internal Memory - See "Memory Buffer." ...
An internal focusing motor enables the camera to focus quicker. If your lens doesn’t have an internal focusing motor it might be able to use the camera’s focusing motor.
For optimum performance in just about any photographic situation, an internal focusing system means that the front barrel does not rotate during focusing. For stability and the use of specialty filters, This internal focusing system is a must.
6 AT-X 242 AF, 15 elements in 13 groups including two aspherical and two SD glass, multi-layer coatings, internal focusing, rotary zoom, 6 blades diaphragm, f/22 min, 80 cm close focus, 1:5.97 magnification, 72 mm filter, ø81.8Ã-89 mm, 690 g ...
Because of the 2500's internal zoom / internal focusing lens there's no extending lens mechanism to get damaged (unlike many other compact digital cameras).
The DF system disengages the linkage between the internal focusing mechanism and outer focusing ring when the focusing ring is moved to the AF position.
8 macro used internal focusing with three independently moving lens groups, meaning the lens length remains constant and aberrations are corrected for all focus distances. At 1x the working distance is 149mm (just under 6").
As you progress and want maybe to buy a more specific lens, look out for lenses with internal focusing motors, like Nikon’s AF-S or Canon’s USM lenses, and with a fast maximum aperture such as f/2.
Tip: The 18-55mm kit lens offers excellent resolution for most snapshots and prints up to 8x10. However, because the D3000 lacks an internal focusing motor, some older Nikon lenses may not focus automatically on the D40, D40x, or D60.
 See also: Lens, Focus, Focusing, Image, Photograph
  
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