[Leica] darkroom focusing

[creativevisions at verizon.net (Michael J Herring)]

Another solution is using a Cold Light enlarger head. You will never have
to
woory about heat and negative "popping". You will also have less dust and
scratch retouching issues.

Mike
----- Original Message -----
From: "Robert Browne" <rbrowne1@mindspring.com>
To: "Leica digest" <LUG@leica-users.org>
Sent: Thursday, June 16, 2005 1:55 AM
Subject: Re: [Leica] darkroom focusing


> 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... ;-)
>
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information


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