Re: [Leica] Apo enlarging lenses

[Kip Babington <cbabing3@swbell.net>]

I'm reminded of the usual advice not to use a lens wide open (if you can
avoid it), but also note that both my 50mm Focotar and 35mm Componon are
already "stopped down" by the factory.  On both, the iris does not open to
the full diameter of the glass.  On the Focotar I'd guess I might get a half
a stop or so more if I could open it all the way, but on the Componon it
looks like I'd get a full stop or more.  Both of these lenses are about 30
years old, so new ones may be different.  But I've always thought it a
curious design "feature."

My most commonly used aperture on the 4.5 Focotar is 5.6, and on the 4.0
Componon it's 4 or 5.6.  This is controlled by the limits on my patience and
the sensitivity of my enlarging meter when using Multigrade contrast filters
- - I try to keep exposures under 20 seconds.  Image sharpness is much more
limited by the fact that few of my negatives are taken from a tripod than by
the use of a less than optimum enlarging lens aperture.

Cheers,
Kip

Mike Johnston wrote, in part:

> All enlarging lenses should be used at the widest stop that minimizes
> aberrations, since diffraction is a far, far worse problem in enlarging
> than it is in taking lenses. (There is a good article on exactly why by
> Ronald B.J. Wisner in a back issue of D&CCT--I can't reference the issue
> just now since I don't have it at home).
>
> You should never stop down a 50mm enlarging lens to f/8 or, worse, f/11.
> If you don't believe this, simply get a very good grain magnifier and a
> negative with crisp grain and WATCH the image of the grain as you stop
> down. Stop down a few clicks and watch the grain magically get sharper,
> then continue stopping down and watch it get mushy again. With virtually
> all lenses there is a quite clear optimum--and it is this aperture that
> you should always use for the sharpest prints.
>