[Leica] darkroom focusing

[rbrowne1 at mindspring.com (Robert Browne)]

Feli,

Aside from the lens focus shift issue, it may also depend on what type 
of enlarger you are using. If there is enough heat from the light 
source and you are not using a glass negative carrier, your negative 
will "pop" during the exposure and go out of focus. One way to test for 
this is to turn on the enlarger for a minute or so, focus your negative 
and then turn off the enlarger. Wait a couple of minutes and then turn 
it back on while viewing the negative through the focuser. If it is out 
of focus when you turn the focus switch on and then pops into focus 
after several seconds then you know that there will be a short duration 
of your exposure when the negative is out of focus.

Remedies are either to use a glass negative carrier (with four extra 
surfaces to clean - forget it), heat absorbing glass between the 
condenser and negative, or compensate by turning on the enlarger for 
the duration necessary to pop the negative into focus (while the paper 
is covered), then exposing your paper for the specified time.

One thing to check is that your paper is perfectly flat. I used to use 
a vacuum easel. Another is that if you stop your lens down too far, 
diffraction can result, which will reduce sharpness. Test to find the 
optimal aperture.

In my experience I've also found that fiber base paper looks sharper 
than RC paper. Make some contact sheets on Azo paper, for example, and 
you'll see a big difference.

Maybe you already know all this stuff. If not, I hope it is useful.

Robert Browne

Feli wrote:

See that's exactly what has me rethinking my methodology. I focus wide
open,
stop down and the grain in the print is not as sharp as I would expect
it to be.
I'm using a good lens, a Schneider Rodagon 2.8/50, but I'm starting to
suspect that
there may be a certain amount of focus shift at work. Just goes to show
you, you shouldn't
believe everything you learned in school... ;-)