> I don't know the details of the specific Pentax macro lens > everyone is talking about but AF lens are often internal focus. So > some IF lens change focal length at close distances as a means of > focusing. So what may be a 100mm lens at infinity may only be a > 70mm lens at 1:1. As a practical matter it would seem that the > only drawback would be losing lens to subject distance faster than > a straight mechanical helicoid lens that just racks out to focus.
Hi, Warren. This is not necessarily just an AF lens "feature": Boz has a discussion of this sort of situation with FREE lenses at http://www.bdimitrov.de/kmp/extras/focalLength/index.html, featuring one of my favorite lenses, the A 100/2.8 Macro, for the example. Fred - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
