Either in a contact printing frame or, at the very least, a meticulously cleaned pane of glass. Dulled edges of course.
"Wubba, wubba, wubba. Bing, bang, bong. Yuck, yuck, yuck and a fiddle-dee-dee." - The Yeti
How to get good contact between the negative and the paper, is a story of its own. (Please search for it, there is plenty of information and I recon, even a subforum here on Apug devoted to it.)
Originally Posted by Existing Light
But when you use the enlarger as a light source, there is a possibility that there is some light fall off at the edges at full opening. Now, "real" contact printers don't use enlargers, only a selection of light bulbs to choose from. Maybe funny, but it's not a joke...
It is easier to focus wide open. Stop down for printing.
Originally Posted by photomem
I agree with Ralph. I've been printing for over thirty years in various formats. My enlarging lenses vary from f2.8 to f5.6 at their widest openings. I focus wide open on the grain and stop down to f8 or f11 to print. Works fine.
If I try to grain focus with any of my enlarging lenses wide open it literally hurts my eyes. And they are mostly f/4 and f/5.6 lenses. I also don't see how to grain focus at the corners with the enlarging lens wide open. Maybe with an apo process lens, but certainly not any of the others that I have used.
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They are quite bright, you are correct, but no problem focusing into the corners.
Originally Posted by keithwms
I use a 300mm Rodagon on my 8x10 enlarger for a light source when making 7x17 contact prints in a contact printing frame. I vary the f stop to vary the exposure time. If I need to dodge or burn this give workable times for such activity. It is much harder than d&b in an enlarger because you can not see the image, just guess or calculate relative to the print frame.
Originally Posted by Existing Light
Ralph, by that I meant (as I am sure you know): some enlarging lenses will not be sharp enough to judge the edges when shot wide open. It's not worth going through lens-by-lens here, but... anyone with a grain focuser can look at corner sharpness as a function of aperture.
Originally Posted by RalphLambrecht
From an optical standpoint, it's not obvious to me that the corner focus you establish with the lens wide open will be identical to the corner focus when it is stopped down. Yes, I am saying that the focus may drift with aperture... at least for some glass. This seems very nonintuitive because we focus wide open through our cameras all the time. I don't know if anyone else has seen this effect, but I did see it with some no-name wide enlarging lens at high mag. Generally it's something that we take for granted, that the lens is sufficiently corrected to give consistent focus through all the apertures. And that intuition is mostly correct... I am just saying, beware. When we judge focus, we do so in relative terms... we compare in-focus to out-of-focus. It's not like bells go off when we hit the focus right on, it's always comparative... and thus your eyes can be tricked. At least by some (inferior?) enlarging lenses.
Of course, the other part of this (and perhaps the more important part in general) is that if the lens is not sharp to the corners when shot wide open then we can unwittingly make some error in determining optimal focus there. So of course... best policy, esp. if you want to enlarge wide open because of shorter times or whatever, is to check multiple points with the grain focuser. And try a few different apertures as well, it may surprise you.
And of course none of my comments are directed at Ralph, though he may wish to say more...
Anyway, just a supplementary word of caution that I think is worth repeating, especially for any newcomers to optical enlarging: if you use a grain focuser, do be attentive to the health of your eyeballs! Your eyes, when adjusted to typical darkroom conditions, are quite vulnerable to bright light, such as through a grain focuser with your lens wide open.... photographers need to protect their most valuable faculty! So be patient and give your eyes plenty of time to adjust.... I didn't do this, just once, and had a painful injury for several weeks. I suppose I burned my retina. Hurt like hell, and there is probably some amount of permanent damage. Best policy, I feel, is to stop the lens down to f/16 or so, then open the lens up gradually.
I see no option. I have a terrible time finding the 'sweet' spot of focus, unless the lens is wide open. My enlarger is not bright enough to pose any danger to my eyes, and it has a neutral density filter built-in, should I ever need it. Also, I mainly use a 20x grain magnifier, which is a dimmer instrument then the Peak with its 10x magnification.
However, your warning is justified and your suggestion is valuable. We need to protect our eyes.
Not possessing a ND Filter in the head of my DeVere, I just dialled in 50Y + 50M + 50C
It meant not only my retinas remained in tact but also I could use sensible f stop settings and exposure times
I found (by chance) that one of my top name German enlarger lenses focus shifted as it stopped down – which came as a bit of an unpleasant surprise.
Consequently, I have retired it to paperweight duties