[Leica] Focotar Report

["Anderson, Ferrel E" <AndersonF@ria.army.mil>]

To Eric:  Your comment that you "..seem to remember being told by someone at
Leica that this lens was at its optimum aperture at f/4 or f/5.6. Hmmm..." :  In
the Leica catalogues of the time, f/8 is listed as the best aperture, but in
Leica promotional literature Leica stated that optimum performance 'starts
already at f/5.6".  I found that stopping down to f/4 resulted in very little
improvement in performance, but stopping down from f/4 to f/5.6 resulted in a
remarkable increase in performance across the field.  Stopping down further to
f/8 resulted in slightly better contrast at the far edge.  I would call f5.6 the
optimum aperture from my resolution tests, but I haven't used it enough in
critical applications to determine if this is in fact true.  Contrast and fall
off are the areas I am concerned about.  My prints made at f/8 and/11 at 8X
magnification were great though.  I just purchased the V35 recently, and haven't
had time to assess it critically.

And to Erwin:  How did the 40m Focotar compare to the APO Rodenstock in terms of
flare and color fringing?  In comparing the 50mm Focotar-2 to the most recent
50mm f/2.8 El Nikor and 50mm f/2.8 Schneider Componon lenses, I found that the
Focotar at f5.6 and smaller apertures showed no veiling flare or color fringes,
unlike the other lenses.  Although these lenses showed superb resolution, which
the Focotar matched or exceeded, the prominent flare and fringing would
certainly affect the contrast of the final print, all other factors being equal.
The 40mm Focotar also showed very little flare and fringing at f5.6 and at
smaller apertures, although slightly more than the 50mm Focotar-2.  Rodenstock
claims in their promotional literature that their APO lenses eliminate color
fringing and flare, an believe me, from what I have seen, they recognized a real
need for it!  But did they accomplish it?

The 50mm f/4.5 Focotar-2 lens displayed its optimum resolution at f/4.5, so it
is a diffraction limited lens.  Further sopping down decreases resolution, but
increases contrast and evenness of light distribution already at f5.6.  Further
stopping down does not increase performance, but it tested better than the other
lenses listed above at f/11 and f/16, and at higher magnifications at every
aperture.  How it compares to the APO lenses from the other manufacturers is
still a mute point that I hope Erwin can help us with. 

Ferrel Anderson
Davenport, Iowa