Equivalent Film Foc. Len.
The Equvalent Film Camera Focal length of the Digital Cameras Focal length
Nikon Digital Cameras are divided into two types. Those with 36mm image sensors (ie same as 35mm film cameras) and those with 24mm sensors.
The full frame 36mm sensors are used by the top of the range cameras. Of these, both cameras and sensors are often called FX. The full frame FX cameras are D3, D3X and D700.
The small frame 24mm type of sensor is used by all the remaining cameras. The cameras and sensors are often called DX as well as those lenses made specifially for them. The 24mm sensor is also know as APS type or 1.8".
If you take a lens of a given focal length (for example 100mm) and use on an FX digital camera, the effect would be the same as a normal film camera. If you used that same lens on a DX camera (24mm sensor), the effect would be like using a lens 1.5 times more powerfull, ie 150mm.
For wide angle, this causes a problem because a traditional wide lens of 24 becomes effectively 36 mill when applied to a DX camera which is why Nikon produced their AF DX 10.5 and AF-s AF-S DX 12-24 mm lenses. The common kit lens AF-s DX Zoom Nikkor 18-55 is effectivly 27mm at its widest setting.