Grain Focusing - discrepancies

[Marco Buonocore]

Steve: The difference of 2mm is between the lens and the negative, *not* the lens and the paper.

 

[Steve Smith]

That will make a lot of difference - ignore previous answer!!


Steve.

 

[Mr Bill]

Marco, I presume you're using VC paper? If so, does a UV filter, say a 2B or stronger, improve the focus situation substantially? (If no UV filters around, perhaps adjust for the softest grade possible.)

I still have the same questions - I am heading somewhere with this. The idea is basically that your VC paper may be sensitized well into the UV range. The enlarging lens probably isn't well-corrected for UV, so the result could be a significant focus error (you can't see the UV light). Ctein explored these ideas in detail in his book.

 

[Mark Crabtree]

Yes. What is you light source, your paper, your filtration, and your enlarging lens (and aperture)? I think your answer will be in there somewhere.

 

[DREW WILEY]

I use a Peak Critical magnifier and it is spot on. Certain cheaper units were OK, but not as useful for
checking corners of the field. But when comparing respective magnifiers make sure they are all on
lens axis. The better units should match. I've seen cases where budget magnifiers either didn't use
a front-surface mirror or attached it with some kind of double-faced tape that eventually shrank in
thickness. But maybe you've got a bad magnifier or two and should test them with live printing, provided you do rest them on a sheet of the same thickness and apply perfectly calibrated enlgr
settings and a very precise lens at optimum aperture. Forget the blue filter thing and the nonsense
that spacing at the easel doesn't matter. You can choose to shave with a double-bit axe too, but
it might make a difference in your appearance afterwards.

 

[pentaxuser]

Oh, and tkamiya: I'm sure that the focus column is not slipping. The Durst 138s is a beautiful machine. I routinely leave a negative in the enlarger for a weekend, and come back to make more prints a few days later and the grain is still as sharp as when I left it. I believe I can almost 100% rule that out of the equation.

Thanks for all your thoughts on the matter.[/QUOTE

I am confused again. When you say the grain is as sharp as when you left it, is this a grain sharp image by eye? If it is a grain sharp image by a focuser then the print should be pin sharp unless the negative is out of focus. Were you saying that the print focused by eye is pin sharp or just better than those focused by the grain focusers?

If the neg is out of focus then maybe the eye which cannot use grain for sharpness is able to correct as far as possible an error in focus in the negative whereas the grain focuser simply sharpens the grain and makes the print focus worse but of course cannot sharpen the lack of focus in the neg itself.

Have you tried other negs that you know have produced sharp prints in the past using the focusers?

pentaxuser

 

[MattKing]

Does the magnification built into the grain focuser have the effect of magnifying any focus error in the instrument?

By that I mean, if the grain focuser is 2mm out, and it magnifies by a factor of 10, is the result the same as a 20mm error in placement of the baseboard?

 

[Steve Smith]

Forget the blue filter thing and the nonsense that spacing at the easel doesn't matter.

It is nonsense that it does matter.

If you think the difference in paper thickness at the base board makes any difference, try to work out how small a change in the negative to lens distance would need to be in order to change the focus point by the paper thickness (or even by 2mm). It is a few microns. You cannot adjust the focus of an enlarger that accurately.


Steve.

 

[Newt_on_Swings]

I guess its just a habit then for me, I still use a sheet of paper (hey it also protects my easel from the metal grain finders!) and if using my Peak 1, I just leave the blue filter in, constantly keeping it in the open position collects dust, and closing and opening it to often shifts the focus at the eye piece.

Also, for the OP, you do not focus with the red filter do you? no one has brought up that point, but I have heard people doing this in their darkroom work flow. I don't know why they would, but some people seem to do it.

 

[Bill Burk]

Here's a thought.

Focusing and printing wide open... Your eye's iris will close down considerably, compared to normal practice where I focus with the lens in same aperture I plan to print, which I try to select as the optimum aperture for the lens.

 

[Marco Buonocore]

Mark Crabtree is right: I should have posted my specs a bit clearer off the bat.

Light source is tungsten - one of the Durst Atlas bulbs made for the 138s. I use all sorts of paper. This test was done on Ilford Warmtone Multigrade RC. I did not use any filtration. When I do use filters, I have an Ilford set of gels. I never focus with filters in (that included the red safelight filter). My lens is one of the newer Schneider Componon-S 80mm with the focus lever on it. I focus wide open. In the future I will focus at a working aperture.

The reason I conducted this test with the lens wide open was that I was hoping it would show a worst case scenario insofar as focus was confused.

The filtration issue - blue filter, yellow filter - doesn't quite make sense to me. Here's the thing: when I focus with my eyes, it's very sharp on the easel. When I focus with the grain focuser, it's sharp but not *very* sharp on the easel. The prints I made on RC paper confirmed that to me. At the moment, this is all I'm worried about.

And pentaxuser: to avoid confusion - if I focus the image with a grain focuser and the grain is sharp (or it appears to be sharp!), and I leave the enlarger for a weekend and come back and check the focus with the grain focuser again, it is still sharp. What I'm saying is that the focus column on the Durst 138s doesn't budge. It's got locking focus and it does its job very well.

 

[Bill Burk]

The critical focusers all have front-surface silvered mirrors, right? If someone had replaced original mirror with an ordinary glass mirror your focus would be quite far off.

 

[Marco Buonocore]

The grain focusers all appear to have the original mirrors. They have that extra shiny look of a first surface mirror to me. Like I said, though - this equipment is second hand. That's the nature of the darkroom these days!

 

[Steve Smith]

I guess its just a habit then for me, I still use a sheet of paper.

The conclusion we came to after getting replies from a couple of grain focuser manufacturers was that it makes no difference. No harm using a piece of paper but no need either (apart from your point about protecting the easel surface).

Gene Nocon - "There is a popular belief that focussing on a sheet of photographic paper placed on the baseboard will give you a more accurate result because it compensates for the thickness of the print. This is nonsense. Save your paper".

And the last page of the thread we had a while ago: (there was a url link here which no longer exists)


Steve.

 

[Mark Crabtree]

Thanks for the more detailed workflow information. I agree that nothing stands out there as a likely culprit. I have a Durst 138 also, and it does hold focus very well. What format were you testing? Your enlarger is set up with the condenser head? I don't understand the focus lever on the lens. Is that to open the aperture?

I thought you must be focusing with the lens open since you are able to focus by eye. That doesn't explain the problem, but is certainly not the normal way to use a grain focuser. I wouldn't expect that much focus shift, and that still wouldn't explain the situation, but it is certainly a variable I would eliminate. Another variable to eliminate is the test negative. I can think of no reason that would be an issue, but I would focus using a real negative, focusing on the grain at working aperture since that is what you will do when making photographs.

I have used a lot of grain focusers over the years and never seen a single issue like you describe, so have trouble imagining 3 (or is it 2 - not entirely clear) that don't work. I see very slight differences between my Critical Focuser and my Microsights, but I mean barely detectable. This could easily be down to adjustment, or just tolerances.

Ctein's book (linked above, I think) describes a way to test focus accuracy while eliminating many of the variables here.

 

[DREW WILEY]

Steve - you have no idea of how accurately I work. On one of my enlarger I actually have a custom
focus telescope for magnifying the grain too, simply because the registered neg holder is about ten
feet above the vac easel, which is solid enough to stand on without deflecting it! Otherwise there are all kinds of potential issues, and they simply have to be isolated one at a time. Yes Bill, I have
seen grain magnifiers w/o front surface mirrors - they shouldn't exist, but do. And certain enlgr lenses are certainly capable of focus shift - one more thing to double-check. And to get a good idea
of the reprentative quality-control of a particular model magnifier, you'd have to compare dozens if
not hundreds of them. Just like buying a try square at the hardware store: bring along a true machinist's square and you'll discover just how very few conventional squares are really square!

 

[DREW WILEY]

To back up to that sheet of paper "nonsense" as you call it, Steve - there's more than one reason
for using a very accurate grain magnifier. For one thing, I print some very big polyester prints, and
nobody is going to confuse them with a damn fuzzy inkjet or even Lightjet. Sometimes I need to
enlarge a 4X5 or smaller original onto an 8x10 dupe chrome or interneg. There is a very precise vac
filmholder involved, carefully selected apo graphics lenses, and meticulous alignment of everything.
When that gets enlarged to a 30x40 print, not only would the hypothetical thickness of paper matter, but rather, I focus upon a sheet of film exactly the same thickness. Otherwise a lot of time
and money would go down the drain! This illustrates the principle involved. Just because typical fiber
based papers can't always reproduce that level of detail does not mean thickness is not an actual
factor!

 

[Steve Smith]

It's not really me saying it's nonsense, it's the manufacturers.

The thread I linked to started off with me suggesting that the paper was not required because I assumed that the designer of the grain focuser would have built this in to the total height making it un-necessary (which is how I would design it). Ralph Lambrecht disagreed but claimed that the paper was not needed.

As no one could find any instructions stating if paper should or should not be used, I decided to ask some of the manufaturers.

Based on the replies we received, it was obvious that I was wrong about them designing in the thickness compensation but that Ralph was right (as far as the manufacturers were concerned) in that it was not necessary to use paper under them.

I don't doubt that you work very accurately considering the size of prints you are making but it would be interesting to see the difference if you focused both with and without a piece of paper printing just an 8x10 section of a 30x40 print.

I don't think that you will see a difference but real life results trump theory every time!


Steve.

 

[DREW WILEY]

Steve, I thought you had some shop skills. And do you think that I go around believing everything manufacturers say, and don't test myself??? I make quite a bit of my living talking to engineers and
telling them how to do things better! I love working with German companies because they listen and
want to do things right. I hate working with large US mfgs because the engineers can improve an
idea, but the CEO doesn't give a damn and will just outsource it to China anyway. Japan is another
story, which involves a lot of "lost in translation" attempting to cut thru all the intense hierarchy until you reach the right people or right division (often worth it). But I never take a manufacturers
word at face value. That's why so many folks do business with me.

 

[pentaxuser]

Well after 5 pages we seem to be no nearer solving the issue. Before you did the test you describe in your original post, how did you focus your negs? It sounds as if eyeballing focus was only done and discovered to be the best when you did the test. Previously I presume you used one of your focusers at random. That is you simply picked one up and focused a normal neg then printed it. Did you stick with the same focuser for all of a particular printing session or stick with the same focuser each time you print and ignore the other focusers?

In examining your previous normal neg prints I presume you weren't aware of a lack of focus when examining the prints and your decision to conduct the experiment was simply curiosity that arose as a result of deciding to try two focusers on the same neg quite by chance? If you had not done this then I assume you would have been quite satisfied with the prints you had previously produced.

If eyeballing is better and for some reason in your case it is, then I presume that until you did the experiment all your previous prints were judged to be OK with focusers until out of curiosity you tried two focusers one after the other and discovered a difference which led you to try eyeballing as well which was then the best method.

If you examine previous prints that I presume you thought to be OK before your experiment and do them again with eyeballing then can you make them visibly sharper in every case?

As you will have noted one of my thoughts was that the neg in question was in fact out of focus. I had this happen to me and produced a print that was fuzzy despite being able to focus the grain sharply. I had to examine the neg under a big magnifier to see that it was out of focus. It wasn't easy to see this even with a 6x6 neg and a big magnifier.

I then tried to improve things with eyeballing and was able to make a slightly better print but I think I was able to do this because the grain focuser was so sharp compared to my eye that in effect the grain focuser was simply sharpening the "out of focus" neg and making the out of focus clearer

pentaxuser

 

[DREW WILEY]

Tip: to really isolate the variable of the paper plane itself, you'd have to expose a sheet of film (not
paper) on a precise vacuum easel. Ordinary paper doesn't lie all that flat on an ordinary easel, and can't pick up enough detail for critical work. You're only as good as your weakest link.

 

[Steve Smith]

I made a vacuum easel at work last week. Not for photographic printing purposes though. It was so we could place a printed sheet (screen printed conductive silver on polyester) under a high resolution video camera to view it on a large screen to look for print defects. The sheet had to be flat because there was minimal depth of field. It works very well.


Steve.

 

[DREW WILEY]

If it was me having this problem, once I determined if one of the magnifiers was correct, then I'd use
the same target system to correctly shim or shave all the others to match. In the past I used my
good one mainly for critical work and had merely OK ones avail for garden-variety work like typical
black and white printing. Now I use only the best one and hope that my progressively arthritic fingers
don't drop it like the cheaper ones! (Knowing it was expensive does make me a lot more careful!!)
If purchasing new, I always assume correction is needed unless a test determines otherwise. The
fine focus on a 138 can slip, but there's an adjustment feature for the tension which can be checked
during maintenance intervals. For super-critical work a helical-focus lens mount could always be added, of course.

 

[Newt_on_Swings]

Steve- thanks for the link, I had a chance to read through the manufacturer's rep's replies. It seemed like they didnt really do any testing of it though (or atleast didnt state that they tested it), and seemed that their conclusions were drawn from their own experiences. I shall try it one day when I have a bit of time, and a very sharp contrasty neg to do it with as I dont have any test pattern negatives.

Drew has a good point with the film, which brings up an interesting question. If you were to use a film with a totally clear base, maybe a lithographic arts film, and were to print emulsion side down, the image would not be as sharp as emulsion side up, with only a tiny difference of the height that the image was exposed at. Unless the totally clear base would effect the light path? But we use glass neg carriers that light has to travel though as well. or maybe I have had too long of a day. lol

 

[Mr Bill]

Tip: to really isolate the variable of the paper plane itself, you'd have to expose a sheet of film (not
paper) on a precise vacuum easel. Ordinary paper doesn't lie all that flat on an ordinary easel, and can't pick up enough detail for critical work. You're only as good as your weakest link.

Drew, It's been my experience, with the few Kodak color papers I've evaluated for this, that they exceeded my needs for detail by a LARGE margin. Way beyond what a 6X loupe could show.

So I'm skeptical about your comment about "ordinary paper" not being able to pick up enough detail. Can you elaborate? Is this from testing, or is it just an assumption?