Digital BW, The Print

pr_roark wrote:
> It would have been better to say "more symetrical" lens.  I'm not 
> sure there are exactly symetrical ones outside, perhaps, 1:1 copy 
> lenses.  The typical SLR "retrofocus" lenses, however, have had to 
> stretch the rear lens to film distance beyond what is optimum for 
> most image quality factors, particularly for film shooting, and I can 
> sure see the differences when comparing them to rangefinder wide 
> angles and SLR relatively symetrical "normal" and medium telephoto 
> lenses. 

There are plenty of purely symmetrical lenses out there. The view camera 
world is loaded with them. The classic dialyte, planar, and dagor 
designs come to mind.

There are few symmetrical designs for smaller formats because of the 
design restrictions placed on lens design by the camera body. 
Specifically, the lens mount is a fixed distance from the film plane. 
For shorter lenses this can require a retrofocus design, which is 
mandatory for SLR cameras (to accommodate mirror travel) but may be used 
to a lesser degree on rangefinder cameras (to accommodate the shutter 
mechanism). The fixed position lens mount will also effect the design of 
longer lenses because of the requirements of focusing in a fixed lens 
mount. So, in general, smaller format cameras (especially SLR designs) 
seldom have symmetrical lens designs. This is one of the reasons smaller 
formats didn't become really popular until after WWII -- when lens 
coatings improved to the point that the many element asymmetrical lenses 
became practical.

I'm just saying, there are dozens of purely symetrical lens designs in 
active use today. Just not in small format cameras. LF photographers, 
from 5x4 up to 24x20, use them every day. I've got three in my pack as 
we speak. Two I bought new within the last few years, one that dates 
from the 1950s (a classic Goerz Red Dot Apo-Artar -- a dialyte design). 
Razor sharp and fully corrected.

 From an engineering standpoint, these old, simple, sharp, contrasty, 
highly corrected designs are really elegant.
--
Bruce Watson