[Leica] sharpness discussion

["Don Ferrario" <don@ferrario.com>]

I have always wondered about something
that may affect sharpness.

Accepted, that the "circle of confusion" discussion
determines the tolerable level of "un-sharpness".  
Even at the practical limit of focusing accuracy,
there is some (small) amount of error, but it is too
small to see - the circle of confusion is too small.

That said, is there a difference in the circle produced
by retrofocus lenses (wide angle lenses designed for
SLRs), vs a lens designed for a rangefinder or other
non-SLR camera.

I have noticed that images produced by my non-SLR's
(including non-Leica) have a quality different from those
from my SLR cameras (all brands).

My un-educated guess is that since the SLR retrofocus
lens must basically "straighten-out" the image so that
the focal plane is moved back behind the mirror, the
angle of convergence in the circle-of-confusion is different.
It appears the circle-of-confusion is bigger (and thus 
less sharpness) in an SLR type lens, all other things
being equal.

Of course, this doesn't matter in longer focal lengths - 
the two are designed the same.  Sure enough, as I
compare longer focal lengths (say, 100mm, for a 35mm
camera), the SLR lenses are just as pleasing.  

As an example, my 85mm and 105mm Nikon lenses
are outstanding.  Yet most (if not all) of the 35mm Nikon
lenses (any of the versions) are not stellar performers.
Of course, the Leica 35mm lenses (to varying degrees
depending on the particular model) are all great units.

Does this "theory" hold technical merit?

don ferrario