Digital BW, The Print

>...
>Keep in mind that as you go up in format lens quality tends to go
>down, just 'cause it's really hard to make a good lens to cover that
>much film real estate.   ...

I have tested a lot of 35mm and medium format (mf) lenses.  While it is
certainly true that it is more expensive to make a medium format (or any
wider-image-circle) lens with resolution equal to a good 35 mm lens, most mf
lenses are, indeed, more expensive.

Bottom line -- most of the mf lenses I've used and tested are about "as good
as" the 35 mm lenses I have, which has included Canon "L" serious lenses.
("As good as" means to me equal central resolution, equal or better
resolution at the 35 mm image size, but usually slightly lower resolution at
the edge of the mf frame -- where size of negative more than makes up the
difference.)  The most consistent differences are that the mf lenses are
more expensive and the 35 mm lenses have a larger maximum aperture.

The major problem I've had with most mf cameras that decreases their on-film
performance is the lack of film flatness.  The curls that most mf backs put
in the film cause the film to pop off the film plane (unless you have a
Contax with 220 film and a vacuum back).  With my Rolleis, I overcame this
problem by shooting only every other frame, so that I never used the film
that had been bent around a roller.  Many newer, straight-film-path mf
cameras are now as good as the 35 mm cameras in this regard.

The only lens I ever tested that would resolve 100 lp/mm, on film, at the
center and edge of a 35 mm frame, wide open, was my 150 mm Zeiss Sonnar that
I adapted to my Canon (so as to make a tilting 150 telephoto).

Probably the softest lens I have in terms of edge performance at f8 is the
45mm Canon Tilt and Shift lens (58 mm image circle with radical retrofocus
design required by TS mechanism).  The 24 TS mm was so bad I sent it back --
fun lens, but just not up to display print enlargements.

The Bronica RF 645 that is now my favorite landscape camera will out-shoot
my Canon on a light tripod and within the 35 mm frame with no problem -- due
to both outstanding optics and -- often overlooked -- virtually
vibration-free leaf shutter.  When I go to the full frame mf, of course,
there is no contest at all.

Given the importance of vibration from focal plane shutters and film
flatness in mf cameras, I often think the focus on lens tests is
over-emphasized.  These other problems, if ignored, wipe out the advantages
of our expensive glass.

Paul
http://www.PaulRoark.com