[MrB]

This thread was from 2007 but, for anyone who might be interested now, a standard lens is one that gives a view similar to that perceived by human vision. Its focal length should be close to the diagonal dimension of the film frame or image sensor. For full frame, i.e. equivalent to 35mm film, the diagonal is approx. 43mm, and Pentax still make such a lens - the Pentax SMC FA 43 mm f1.9. For an APS-C sensor, the diagonal is approx 28mm (27mm for Canon), so the closest to a standard lens would be one with 28mm focal length. In practice, lenses up to 58mm (FF) and 40mm (APS-C) have usually been regarded as being in the standard range.

Philip