Without waiting for the digest, it hit me on the way home tonight, and Debbie provided the clue when she sent me a frame she shot with a 50mm lens. (nice shot, BTW) The image scale is too small (with extremely short f.l. lenses) to even worry about differential refraction causing tracking errors on different parts of the frame. It shouldn't be a problem at all. Thanks Debbie! __________________________________ Do you Yahoo!? Yahoo! Mail - Find what you need with new enhanced search. http://info.mail.yahoo.com/mail_250