In article <5omlvr$347$1@taurus.fccc.edu>, r_katz@retro2.fccc.edu says...

>What is the rule of thumb for which projector
>lens focal length is best for image quality?
>I am mainly interested in a quality image
>rather than size.The projector to screen
>distance is about 7 feet; the viewing
>distance is thew same.

As with camera lenses, the FL (related to
format...) determines the angle of view,
not the image quality. At 6-7 feet I prefer
a 60-70mm projection lens, but find the
mis-match with the standard condensers
results in some illumination roll-off...
A high-quality 90-105mm lens may match
your condensers better, and the smaller
image should look sharper.
Hope This Helps
(David Ruether)