Questions about grain focusersgreenspun.com : LUSENET : B&W Photo - Printing & Finishing : One Thread
I am interested in what people think is a good, but not too expensive grain focuser with the following qualities:
1. Bright images
2. Easy to focus grain sharply
3. Very clear image view (achromatic lenses)
-- Dan Stanley (email@example.com), June 24, 2000
Before you get a grain focuser, I suggest you pick up Ctein's "Post Exposure" and read it. Grain focusers have some big problems.
-- Terry Carraway (TCarraway@compuserve.com), June 24, 2000.
I use a Micrsight, it works for me!
-- Robert Orofino (firstname.lastname@example.org), June 24, 2000.
I would like to support Terry's recommendation, although I would reword part of it: Grain focusers MAY have some big problems which, however, are related to their use with VC papers. Ctein's book "Post Exposure" is worth reading anyway, the problem with grain focusers actually being a minor issue in comparison to the other interesting issues he tackles.
Personally, I use a very simple no-name brand which does not exhibit the problems addressed by Ctein to any noticeable degree. That, and the problems reported in the above book, show that a great brand name will not be the end of all problems.
-- Thomas Wollstein (email@example.com), June 26, 2000.
Like Thomas, I use an el cheapo grain focuser that I got from Spiratone 31 years ago and it works just fine. For 8x10 Ilford MG prints this will get me right on the grain. For 16x20 size prints from 35mm and my 29 year old F4 50mm el-nikkor, I will make a small correction. In this case, I focus on the grain at the center and them move the lens toward the negative while watching the grain go slightly out of focus. Then I stop down to at least f8-11 and check that the center has sharpened up. This seems to deal pretty well with what is apparently a slight curvature of the focus plane, and/or the slight curvature of the negative that shows up at these high magnifications.
With my 2 year old 80mm f 5.6 el-nikkor, I don't make this adjustment. Getting the 120 film flat in the carrier is the big issue with the longer lens at 16x20 or larger.
-- Gene Crumpler (firstname.lastname@example.org), June 26, 2000.
I've used focus magnifiers from Scoponet, LPL, and Paterson. Of these I was least impressed with the standard Paterson design, but they make a long-reach or "jumbo" version which makes top-of-the-column prints much less of a pain in the neck. IMHO any grain magnifier is a darn sight better than no focus aid at all, provided it's properly adjusted to your eyesight.
There used to be simple ground-glass focussing boxes available. These were a little metal or Bakelite box which held a mirror and a ground glass screen at an angle suitable for viewing, without leaning over the easel. I haven't seen one that incorporated a magnifier, but it wouldn't be a difficult modification. This would eliminate the problems that some people seem to have in focussing an aerial image.
-- Pete Andrews (email@example.com), June 26, 2000.
After re-reading this thread, and particularly Pete's answer, I returned to Ctein to refresh my memory of his findings.
For one thing, I have to correct my own answer further above a bit. I said the problems with grain focusers are linked to VC paper. There should be a nowadays somewhere in that sentence. There are actually two problems with grain focusers, one owing to the characteristics of the human eye (which is consequently independent of paper type) and one owing to the spectral response of the paper. (Yes, that's the one that is specific to VC paper.)
Our eye has a serious problem with the focusing of deep blue light. You may have noticed manifestations of it by lloking through deep blue filters (focusing causes strain on the eyes) or at blue neon signs. With older enlarging lenses, it seems to have been useful to focus with a blue filter because the lenses showed considerable longitudinal chromatic aberration (LCA). The paper, however, is mainly sensitive to blue light. So if you focus with the blue filter, you focus with the light the paper is sensitive to. Yet, due to our eyes' LCA problem with blue, you may have driven out one devil with another. Modern lenses are not a problem in this respect as their correction is better. So NOWADAYS, focusing through a blue filter is not so common any more, and it doesn't get you anywhere but in trouble. So much for the general problem.
The problem of VC papers is not so easily explained. It is related to the spectrum of the light generated by your enlarger (most notably contributions at short wavelengths), the correction of LCA in your enlarging lens, and characteristics of the paper which may all act in one direction to give you a serious problem. This problem, however, is not related to the kind of focuser you use, i.e. it is the same with an aerial-image focuser and with a ground-glass focuser. It is also not related to the quality of lens correction within the domain of visible light as it is caused by UV light. Ctein reports that some of the worst problems were found in expensive APO lenses (which were great with visible light). Fortunately, however, the problem only affects a minority of printers.
Ctein proposes a simple test with the negative sandwiched between sheets of glass to exclude negative popping as a source of fuzziness: Put your easel on a 5-mm stack of cardboard. Focus. Print #1. Remove cardboard stack. Print again w/o re-focusing, #2. Put easel on 10-mm stack. Print again w/o re-focusing, #3. Put easel on 5-mm stack. Print again w/o re-focusing, #4. #1 and #4 should be equally sharp. (If they are not, the focus has shifted during the procedure.) #2 and #3 should be less sharp than the others. (If they are not, you've found that you have got the problem.)
As the problem is related to short wavelengths, it is less likely to occur when your enlarger uses tungsten light. Quartz lamps and vapour lamps are more likely to produce considerable amounts of UV light.
-- Thomas Wollstein (firstname.lastname@example.org), June 28, 2000.