[Leica] darkroom focusing

[feli2 at earthlink.net (Feli)]

Thanks for all of the helpful information Robert. I am using a 
Saunders/LPL diffusion enlarger, without a
glass negative carrier. I've seen the heat 'pop' you are talking about, 
so I have been working at a smaller
stop to cut down exposure time and be closer to the sweet spot of the 
lens. A glass carrier is on my
list, but I'm thinking about switch to a VCCE enlarger, so I'll first 
have to see what I end up with.

Cheers,

Feli


On Jun 15, 2005, at 10:55 PM, Robert Browne wrote:

> 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... ;-)
>
>
> _______________________________________________
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>
>
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feli2@earthlink.net                     2 + 2 = 4                      
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