In article <4bs1kp$j1a@merlin.delphi.com>, lhabes@mci.newscorp.com says...
>I have had some problems getting my entire picture to stay in focus >even though the objects in the picture seem to be around the same >distance. The objects around the perimeter of a slide focus at a >different focus setting on a projector than objects at the center. Is >this some form of spherical abberation?

The focus and sharpness of the taking lens and of the projection lens
are different and independent, though problems with the latter can
make you think you have problems with the former. If you can refocus
the projector lens to focus the edges of the slides, the problem is
a common one: slides are not held flat in the mounts. Partial cures:
remounting the slides in glass mounts (ugh!), or replacing the projection lens with a "curved field" type.
Hope this helps.