RE: [Leica] Which Ultra-Wide, Heliar 15mm or Heliar 12mm

["Rodgers, David" <david.rodgers@xo.com>]

Henning,

Thanks much for your post. All very good information. I think this gives me
some of the answers I was looking for. I really like the Heliar. I just
stopped using it for a while because I was having some problems with it,
particularly with chrome film. I had some sharpness as well as exposure
issues. Diffraction may have been the culprit. I try not to go beyond f11.
Even that may be stopping it down too much. 

Dave

>>In my experience super wides need a little more exposure, partly due 
to the fact that since such a large solid angle is imaged and both 
near and far are often important components of the image, the 
contrast range tends to be greater than with longer lenses. Combine 
this with the larger amount of light falloff to the corners, and you 
then need even a bit more exposure overall. I usually give 1/3 to 1/2 
stop more exposure with slide film and another 1/3 with negative film 
when using the 15 or 12, compared with metering the same surface with 
a 50. The 21's generally need an additional 1/3 stop at most.<<