Archived posting to the Leica Users Group, 2005/06/15
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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... ;-) > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information > > ________________________________________________________ feli2@earthlink.net 2 + 2 = 4 www.elanphotos.com no archive