On Mon, 17 Aug 1998 19:01:46 -0800, tired.of.spam@nospam.com (Rudy Garcia) wrote:

>A diopter closeup lens including two element achromats, will not give you
>excellent sharpness corner to corner, even with the main lens well stopped
>down. [....]

Um, with a "happy" combination of achromat (2-element close-up
lens) and standard (or macro) lens, used at smaller stops, excellent
corner sharpness can be had. BTW, I've had good luck adding
a compatible 1.4X or 2X converter to the combination of lens +
achromat for even greater magnification (some samples of these
with up to 3X magnification with good sharpness and DOF are on
my web page, in the "Bugs" section, under "Phun Fotoz"...
[or just go to:
http://www.fcinet.com/ruether/web_photos/phun_fotoz/bugs/b55.jpg
if you want to miss the rest of my BEE-YOO-TI-FUL web page...;-]).