On Mon, 5 Sep 2005, Godfrey DiGiorgi wrote:
A D-FA50 macro lens is designed to be best at flat-field imaging, stopped down to f/8-f/32, in the near-focusing range. An A50/1.4 is designed for general pictorial use at wide apertures, and will not perform at its best at copystand distances.
It was either in the general Pentax lenses and accessories booklet or the manual of the 1.7x AF T/C that I read that the 50/1.7 is recommended for macro work with extension tubes; the 1.4 was recommended against.
Kostas
