Grain Focusing - discrepancies

Marco Buonocore · Oct 20, 2012

Hello,

I've got a problem. I was curious about my grain focuser - a Micro Sight II. I compared it to a Micromega Critical Focuser (the high end Peak ones). The two focusers were different. That was disconcerting. So I grabbed another Micromega Criticla Focuser, and a Peak Enlarging Focuser II. Guess what. All slightly different.

Truthfully, I don't really know how these things work. They're one of the few pieces of equipment in the darkroom I trust blindly. For them to all give differing information; well that is no good.

To preface: I use a glass carrier in a Durst 138s. I keep my enlarger aligned with a versalab alignment tool. I'm confident all is good on that end of things.

So here's what I did. I have one of those "test pattern" focusing negs. The one in question is made by Jobo. I loaded it into the carrier, and made a 5x7 crop from a relatively big enlargment (12x16 ish). I marked each of the four grain focusers, and made RC prints from each focusing as sharply as I could on the same spot on the neg. I also made one print where I focused by eyeballing it. I made the exposures with the lens wide open, hoping to take depth of field out of the equation as best as I could. I batch processed the prints and dried them.

I went through the 5 prints, and ranked them in order of sharpness. I gave them to my girlfriend, and she did the same.

The results? The eyeballed print was - by some margin - the sharpest. We both came to that conclusion.

This has me dumbstruck. What is the point of the grain focuser if the information it provides is not reliable? Those Micromega Critical Focuser are supposed to be high end tools. They sell for a small fortune.

The problem is, while it's easy to eyeball and focus these "test pattern" negs, it's not so easy to do the same with an overexposed shot from a Holga lets say.

I'd love your thoughts on this. Is the "test" valid? How can I remedy the situation?

Thanks!

CatLABS · Oct 20, 2012

Who cares if an over exposed holga shot is critically sharp?

Newt_on_Swings · Oct 20, 2012

Did you happen to follow the manufacturer's instructions on setting the focus of those grain finders/focusers? Also did you place a sheet of paper under the finders the same thickness of the paper you are printing with? Another issue can also be vibration after focusing.

I have used a number of finders in the past, my favorites are the 25x microsight and my peak 1 focuser. I have also used the hocus focus sometimes which works fairly well with such a simple design. The larger peak helps with viewing corners. It also has a blue filter which has been debated about its effectiveness.

tkamiya · Oct 20, 2012

Did you calibrate your grain focuser? If you look into a grain focuser, you will see a hair either going across or in X shape. You should also be able to twist your eye piece. You are supposed to turn your eye piece until the hair is critically in focus. Then you could use your focuser to focus on the projected grain.

I have seen focusers with this hair missing. There's no way to calibrate that....

Gerald C Koch · Oct 20, 2012

Unless you expose prints with the lens wide open you should not have a problem. Once stopped down the depth of field should make any small inconsistencies meaningless.

ic-racer · Oct 20, 2012

I'll gladly take all the bad ones.

Bob-D659 · Oct 21, 2012

If you don't adjust the eyepiece on the grain focuser to match your eye, do it with the image WAY out of focus, then the focus on the print should be almost perfect. Otherwise it could be way way off, especially if you are young and have eyes that will adaptively focus too easily.

Steve Smith · Oct 21, 2012

Newt_on_Swings said:
Also did you place a sheet of paper under the finders the same thickness of the paper you are printing with?

We busted that myth a couple of years ago. I contacted some manufacturers of grain focusers and the conclusive view was that it doesn't make any difference.

The depth of focus at the paper is quite large whereas the position of the negative is very critical. You cannot move the negative with respect to the lens with enough precision to make any difference as small as the thickness of paper.

Steve.

tranquibra · Oct 21, 2012

Eyeball focusing will get tougher and tougher as we grow older, especially after spending longer time in DR under the safe light. As long as the same unit can yield the consistent results, it should be OK. Of course, sometime it could be a little frustrating when grains are too fine.

Marco Buonocore · Oct 21, 2012

So, to answer some questions: Yes, I did calibrate the grain focusers to my eyesight. The Micro Sight and Micromega Critical focusers make it relatively easy to do. So that's taken care of.

I didn't use a piece of paper under the focuser. But that was consistent. I didn't put paper under *any* of the focusers. It doesn't explain why the results from the four instruments would differ.

For Gerald Koch: You say that if I stop down, there shouldn't be a problem. I respect that, but it still bothers me. Surely the grain is either in focus or it isn't. I do have a couple of negatives that I have to print wide open, particularly if I'm doing a large enlargement. When I'm lith printing, I routinely print wide open.

Is there any way to calibrate a grain focuser other than by adjusting it for your eyesight? I suppose there really isn't.

Sal Santamaura · Oct 21, 2012

Have a look at page 76 here:

http://ctein.com/PostExposure2ndIllustrated.pdf

Bob-D659 · Oct 21, 2012

Marco, no there isn't, unless the grain focuser projects the image onto a piece of ground glass. Even then you still have to adjust the eyepiece so you see a clear image.

As you get older, the eye loses it's ability to switch focus points quickly, then you will find the grain focuser becoming more accurate. or depending on your point of view. Years ago, Zeiss made a special focusing telescope so their (mostly younger) technicians could accurately align microscope camera focusing units that used an aerial image in the same way a grain focuser does.

Marco Buonocore · Oct 21, 2012

Sal: page 76 seems mostly to do with using blue filtration, which I'm not doing. I understand the difference between ground glass and an aerial image focuser. I'm not seeing too much else that helps me.

I just don't understand how four instruments designed to tell me one things provided four different answers. It would be like having four calculators, giving them the equation 2+2, and coming up with the answers 3.75, 3.9, 4.1 and 4.3. You wouldn't say "well, that's close to 4. Good enough."

I'm not particuarly young, but I was really surprised by how much sharper the prints focused by eyesight were compared to the grain focuser.

While it's much easier to focus with a grain focuser (everything snaps right into place, doens't it?) it's of no use if it is not accurate.

Bill Burk · Oct 21, 2012

Sounds to me like you should focus by eye... Make print and develop to confirm it's still best... then without changing the focus, put the grain focusers down to see which ones confirm the focus... If the direction of error is "up" you could put something significantly thick under the focuser to correct the error. (But if the direction is "down", you're stuck there).

ic-racer · Oct 21, 2012

Bill Burk said:
Sounds to me like you should focus by eye... Make print and develop to confirm it's still best... then without changing the focus, put the grain focusers down to see which ones confirm the focus... If the direction of error is "up" you could put something significantly thick under the focuser to correct the error. (But if the direction is "down", you're stuck there).

If they really are off they will need to be lifted or sunken a few millimeters if not centimeters to see any difference.

I'd suggest just adjusting the eyepiece on all of them. I suspect the issue in the OP is in correctly viewing the aerial image.

Bob-D659 · Oct 21, 2012

Again Marco, a grain focuser that isn't set to one of your eyes specific vision, with or without corrective lenses is worse than useless, as you have already demonstrated.

Assuming the mirrors haven't been replaced, knocked out of position, the crosshair is in the factory aligned position, the frame isn't otherwise bent, spindled or mutilated, the optical adjustment to the user's eye is just plain off unless the user has uncorrected astigmatism when using the grain focuser

pentaxuser · Oct 21, 2012

Very frustrating and I can't explain why you have experienced what you have and if it's any consolation to you it would seem that none of us, me included, can give an explanation that resolves the issue. Bob-D659 has really covered all the likely issues but if none of these apply then I am stumped.

I have two Paterson grain focusers. The micro and the major which is much taller for large prints. It avoids bending down over the print while trying to adjust the focus. There is a very marginal difference between the two so minor differences may not be unusual but not ones that show up on a print that I can see although I should add that my biggest print is 8x10

However as your best print is the eyeballed one then it may be that your best bet is is to obtain a Kaiser focuser or the Nova Darkroom one called I think a Hocus-Focus or some such comical name. Others here who have got one may know the correct term.

Both work on the principle of simply magnifying the projected print instead of focussing on the grain. I have the Kaiser as well and I find that it does as good a job as the Paterson if you find a line that demarcates light from dark such as a window frame. Both will also do their jobs into the corners of the projected image

Before selling all your grain focusers however just make sure there isn't an explanation and solution that you have overlooked. It'd be a pity to sell all your grain focusers only to find that there was a solution.

Best of luck and I hope someone can suggest an answer

pentaxuser

AgX · Oct 21, 2012

Bob-D659 said:
..., the optical adjustment to the user's eye is just plain off unless the user has uncorrected astigmatism when using the grain focuser

Could you explain more? Seems interesting.

tkamiya · Oct 21, 2012

I'm finding it difficult to believe there is THAT much difference between different focusers. It's quite a significant difference to be able to see on print and have an agreement between two people.

Going 35mm (I am assuming) neg to 12x16 isn't all that unusual.

I wonder if there is another factor involved. Say you focus carefully with a grain focuser. The focusing stage could drift a bit and the image goes out of focus. Something like that? Can you carefully focus the image with one focuser. Let it sit there for 30 seconds or so then look again. Is it still in focus?

It is true the DOF at base board is quite big. But the focuser is used to adjust the distance between film stage and the lens stage. This adjustment is quite critical.

I'm amazed you can actually do better with your naked eyes. I cannot. Not even close.

Bill Burk · Oct 21, 2012

tkamiya said:
It is true the DOF at base board is quite big. But the focuser is used to adjust the distance between film stage and the lens stage. This adjustment is quite critical.

I forgot about that, you're right.

But as you focus, the distance from lens to baseboard also changes, this complicates things a bit.

Mr Bill · Oct 22, 2012

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.)

pentaxuser · Oct 22, 2012

One other thing that tkamiya's post has reminded me of. Check the movement in the enlarger bellows.There should be a screw that allows you to tighten the bellows so after focusing they don't move. Movement can be a problem if the print size means that the bellows are tightly compressed. I have had this problem with my Durst 605 and need to tighten the screw so that focusing knob is stiff to move.

It is possible that you correctly focus with each focuser then the bellows move slightly before you expose. In the case of the eye-balled print, was this the last print to be made? If it was and you focused by eye then instantly hit the expose button the bellows might not have had a chance of moving so that one was the best.

Just a thought

pentaxuser

BMbikerider · Oct 22, 2012

There is a book of which I have a copy (now out of print) by the late Canadian Photographer, Gene Nocon. He goes into this focussing lark in some depth and recommends the use of a blue filter over the focussing magnifyer eyepiece lens because the light from the enlarger bulb tends towards the red end of the spectrum and the paper is at the blue end. Using a blue filter over the lens allows the light rays to focus on the actual paper which is blue sensitive as well.

He is using a Peak focus finer in the book illustrations and this has a blue clip on filter for the eyepiece. I do find that it does make a very slight difference so I use the same technique, but calibrate my diachronic filtration in the LPL enlarger head to give me a blue light for focussing. I suppose if you are well off enough to afford an APO lens this does not matter.

Marco Buonocore · Oct 22, 2012

Well, I looked at things with a fresh set of eyes today. I roped in some of my colleagues in the darkroom as well. My conclusions were the same; the prints focused by eye were sharper. You really can't miss it on the test negatives, because of the series of fine lines, swirls, etc... I should scan these so people can see what I'm talking about. But it's quite apparent. The test negs are rather brilliant for that; errors in focus stick out like a sore thumb.

I then focused the test neg by eye, noting the column height. The grain focusers were focusing roughly 2mm closer to the neg than I feel was correct. The durst column has these markings, so it's not too hard to see. Another thing I did was re-focus by eye, then go through the whole range of adjustments (from lowest setting to highest - it's helical focus) of the grain focuser eyepiece. Never did it look visually sharp. Not that critical sharpness I see when I move the lens 2mm closer to the neg.

So, what Bob-D659 says is relevant. Maybe all these grain focusers have been dropped, or had glass replaced, etc... Who knows. It's all old equipment. None of it was bought new, I don't think. I doubt it, personally, but it is possible.

I did a quick and dirty test to see where the base of the grain focuser had to be in order for it to jive with my focusing by eye. It looked like it needed to be 5mm to 10mm higher off the baseboard. I loathe the idea of shimming a grain focuser.

Perhaps the more mathematically sound members can determine weather this approximate 2mm difference will be apparent visually when making a print, stopped down to a working aperture.

My feelings are why go to the trouble of using a glass carrier, aligning my enlarger, etc... if my grain focuser is slightly off?

Sometime this week I reckon I'll get my eyes checked to see if I've got astigmatism or whatever it's called. Maybe I'll post a follow up with those results!

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.

Steve Smith · Oct 22, 2012

Marco Buonocore said:
Perhaps the more mathematically sound members can determine weather this approximate 2mm difference will be apparent visually when making a print, stopped down to a working aperture.

Not sure about that. However, when it is properly in focus, a 2mm difference in paper height will not be noticeable.

In his book, Edge of Darkness, Barry Thornton did an experiment. He put his easel on a 1/2" thick piece of board then focussed normally and made a print. He then made a print without the 1/2" board and another print with two boards. He says that he could see no difference in the sharpness of the prints 1/2" either side of optimal focus - and he was a sharpness fanatic!

So basically, a 2mm difference will not be discernable - however, you do need to be focussed first, and this is where you are having problems.

Steve.

Grain Focusing - discrepancies

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