Do I get the conclusion right then, the blue filter is only useful for non-APO lenses on graded paper with flourescent light source and only if your eyes are more sensitive to infrared than average?
That pretty much sums me up. So that filter will probably work for me but nobody else.
I would have to dig thru the closet but someone else had done an article about this very effect in 'Photo Techniques' or ' Darkroom & Creative Camera Techniques', conclusion was that white light focusing has the best chance of hitting the mark.
Several problems not addressed by Ctein's book:
focus accuracy of the grain focuser, was it ever deopped?
color correction of the eye piece in the grain focuser
blue filter on the eye piece, below the neg OR above in the light path?
UV output of the light source
naked eye vision differences
UV reaction of the papers
Where to focus, dead center or 1/3 out to the corners?
APO should mean NO LCA, I guess several companies lied just a wee bit
Virtually all lenses display LCA and stopping down does reduce it, usually by f/11
Virtually all lenses display field curvature and stopping down does reduce it, usually by f/11
Is f/11 past the diffraction limit of the lens? or would it actually matter.
Seems to be much ado about nothing
Originally Posted by ic-racer
Well, I have read Ctein's book,now free for download,and it details processes and materials that have now retreated into the misty veils of history.
It does detail a truly grisly ,and documented detail, of what can happen to an RC print when it is glassed and framed.
I suspect it is now in the public arena because nearly every paper and film he mentioned is now extinct.
Two things I did note,which may still be relevant : Of the many enlarger lenses he tested, very few did not produce their best resolution at much below 1Fstop below maximum aperture.
And,he suggested trying a 3 print test : best focus/,easel raised 5mm,/easel dropped 5mm. Pick the sharpest print.
I'm pretty sure I mentioned the Gene Nocon "I used a blue filter on my focus magnifier and it raised my print quality to a new level" idea some years ago on this forum : predictably, a heap of largely negative responses.
None,I think,from anyone who actually tried it.
Pure conjecture here, but color-blindness is much more prevalent in males,and this forum is predominantly male - anyone of a curious bent could always try it.
If it makes no difference,ok. If it does- say so.
Barry Thornton documented this in his book Edge of Darkness. Except his test was more like +/-15mm rather than 5mm (could have been 1/2").
Originally Posted by Smudger
He couldn't tell the difference and he was obsessed with sharpness.
Originally Posted by Smudger
I have also raised this point. Also Gene's suggestion not bother with a piece of paper under the magnifier which also received many negative responses despite the fact that it is not needed as proven by the point above and by a couple of responses from grain magnifier manufacturers.
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Some of the posts seem to be confusing the two LCA issues Ctein discusses, the first being the Patrick "Gainer effect", why blue focusing is bad etc, and the second, more disturbing one I was referring to - ie combined focus error caused by VC paper UV sensitivity and residual UV range LCA even with APO lenses.
As I said earlier just for the hell of it I'm going to run his suggested test. It's (hopefully) a curiosity more than anything as my prints look pretty sharp to me. Although as I said earlier I'm usually in the grade 2 range so it's possible I haven't had any apparent problems with this simply because I can't remember the last time I used a high contrast setting (say grade 4 or higher).
I'm still puzzled by the whole thing. I'm not trying to be an alarmist or a grain counter or anything. But I just thought it was an interesting issue because it raises the following points in my mind regarding this LCA effect:
1. Suppose none of us are experiencing the rather gross errors like 15mm or whatever (again, to me this seems gigantic for an 8x10 enlargement of a 35mm neg, which was Ctein's example), but rather smaller errors that we aren't necessarily noticing in our prints. It would at least highlight the futility of debates regarding which APO enlarging lenses have the highest resolving power. Even a small focusing error is likely enough to obliterrate the last few lines/mm of resolution we think we're getting. So if nothing else perhaps we gain some perspective. I mean, some of us like to admonish people for being grain counters, but in the end most if not all of us use grain magnifiers to focus, right?
2. Ctein's experiments indicate this focus shift, if it exists, increases as we allow more blue light to hit the paper (ie higher contrast filters). So while say a straight grade 2 print might not have much of a problem, what about people who use split grade all the time (ie always mixing 0 and 5)? It seems to me this would be the worst case scenario since the the focus shift between the grade 0 exposure and grade 5 exposure would be at its maximum.
The filters that are magenta and yellow, both dichroic and condensor setups that I use .
I keep hearing blue light what does this refer too?
I have not noticed a focus shift with grade 5 filter .
Thanks for bringing this back to your original post, Michael. If you do try this test out before me, which seems likely, I, for one, would be very interested to here your results. What shouldn't confuse people is that results vary and that no test of this can bring about a general statement on this issue (as said in Ctein's article). Sure, as said, we are looking at critical sharpness, but, if it is 'grain peeking', it is the type of study into the detail that has made any darkroom material discussion all the more enlightning for individuals. By no means do I try to use the theoretical optimum methods available which are discussed on the forum and many don't interest me, it's just interesting to make simple tests from time to time and either tweak what I do, if there is no major upheaval involved, or carrying on regardless.
As a related aside, I have 3 grain focus devices: a short Paterson one which I used for years, now shelved because a longer Paterson Major gave me critically sharper results and the third is a Kaiser focus scope which gets to the edges of an enlarged neg. I would not be as happy using my older device now knowing what I do, even though it was adequate: a small improvement, but a significant discovery for me.
The more magenta, the more blue light gets passed and the more green light gets absorbed/reflected (depending on whether dichroic or not). Since the blue sensitive emulsion is the high contrast emulsion in VC paper, dialing in more magenta increases contrast.
Originally Posted by Bob Carnie
The more yellow, the more green light gets passed and the more blue light gets absorbed/reflected. Since the green sensitive emulsion is the low contrast emulsion in VC paper, dialing in more yellow decreases contrast.
Last edited by Michael R 1974; 08-02-2011 at 10:16 AM. Click to view previous post history.
I may or may not get a chance to try this tonight. I'll report my results if I do. For the longest time I used a simple Paterson. No problems. I switched to a Peak a few years back because I wanted the ability focus further away from the center of the image. It's a very nice piece of equipment, but I don't want to overstate its worth.
Originally Posted by chimneyfinder