1800/f#

[bercov@xxxxxxxxxxx (John Bercovitz)]

> res=1800/f# makes assumptions about the lens (probably that it is
> otherwise perfect) that may not be true in real life.

That's correct (of course 8-).  This is the resolution limit in terms
of plate scale for a resolution-limited lens.  I haven't seen any camera
lenses that will do it.  Camera lenses cover a larger field and telescope
lenses tend not to.  So there is hope with a telescope of being diffraction
limited over the area covered.  There are aberrations which get better as
you stop down a lens and some rare ones which get worse.  At f/32, I
think you can get within a factor fo two of the physical limit.  Same
at f/16.  At larger apertures, it gets worse in terms of realized/theoretical.

John B