Grain focuser recommendation

DREW WILEY

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What happens when the humidity changes, and the paper thickness swells? Do you tear a few pages out of the book, or just remove the dust jacket?
 

Bill Burk

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DREW WILEY said:
What happens when the humidity changes, and the paper thickness swells? Do you tear a few pages out of the book, or just remove the dust jacket?
Click to expand...
Right. Forgot to specify. Seventh printing, 1981 - caliper reads 0.885 inches at the coast on this foggy day.

So the actual depth of focus is 0.0995 inches - Wild how close that is to a tenth of an inch.

But it’s not a half inch as I think Ctein wrote.
 

ic-racer

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Bill knows, just raise your magnifier until it is blurry and see how far off the table you can get it.

Or, if you like math, this optical formula predicts about a 2mm focus spread on the paper side, at f2.8 at 9x enlargement. This easily encompasses any photographic paper of which I am aware. (it is a reconfiguration of the view-camera focus equation taking into account Airy disk size and circle of confusion.)

Modular transfer function focusing equation (equation #38 in http://www.largeformatphotography.in...DoFinDepth.pdf) :
N_max ~ 20 / (1 + m) sqrt(dv)

N-max = F number
m = magnification
dv = focusing leeway on the baseboard
20 = constant for circle of confusion about 0.15mm on the print
 

AgX

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So far no one mentioned that there are two kinds of grain-focusers:

-) with a ground screen

-) with an eyepiece focussed on the aerial image

The former is most easy to view,the latter gives brighter image with higher resolution
 

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Cannot agree with this approach. Enlarging is focusing on a plane, any suggestions that shifting that plain by ANY amount is prudent is ... plain wrong. Same applies to scanning on flatbed scanner, none of which are made to exacting assembly standards, where a single thickness of copy paper under film holder CAN make a difference in achieved scanned resolution.

In other words, allowing DOF to play the game in 3D world is one thing, to knowingly let it slip in in a 2D environment is just lazy, especially when it takes nothing to place that grain focuser where it is meant to be. I don't need to see or not see a difference between the two, as I see no reason to even argue about it.
 

MattKing

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I think you missed the point of what I said.
Grain focusers permit you to more clearly see whether an enlarged image is in focus.
If a change to the position of the focuser makes no difference in what you can see with that grain focuser, than the change of position won't affect the accuracy of the results.
Once depth of field (or is it depth of focus?) comes into play, the "mark I eyeball" is the limiting factor here - there is no way to determine which of the two measurements - with the paper in or with it out - is more correct than the other one, if there is any difference at all.
It may be true that there are different tools out there that can more accurately determine the exact centre of where the plane of focus is. But they aren't available for sale as grain focusers, and most likely won't result in any measurable differences to the quality of your prints.
 

DREW WILEY

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Here's an example of what can go wrong. A long time ago I started out with a cheap Omega magnifier which was shimmed on the base with cardboard, which is not a dimensionally stable material. It started out vaguely accurate, but over time the cardboard swelled, and the cumulative result over time with that what appeared to be in acute focus was in fact objectionably way off, out of plane. My own philosophy about this is to do with all that "circle of confusion", "allowable" in-focus/out of focus talk exactly what I did with the cheap magnifier - relegate it to the trashcan.
I don't want so-so OK focus, combined with so-so plane flatness, combined with a so-so un-flat negative. I want everything correct. And once your enlarger is properly aligned and you take things seriously enough to use a good glass carrier, then PRECISE focus is no more work than being sloppy about it - in fact, it's far easier and quicker, and certainly more dependable, hence cost-saving with respect to paper usage.
Furthermore, enlarging lenses are engineered to work best within a particular f-stop range. I won't go into details about that here. But if one is counting on stopping it further and further down on a guesswork plus/minus basis, or due to sloppy planes or an uneven neg, they're paying a qualitative penalty all around.
 

Andrew O'Neill

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Back when I was enlarging a lot, I always made sure the three stages were aligned (especially with 16x20). I always used a piece of the same photo paper that I printed on. I didn't skimp on the grain focuser, either. Peak Omega Micrograin focuser.
 

DREW WILEY

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I cut my teeth printing big Cibachromes up to 30X40 inches, which was a medium capable of holding tremendous detail, yet also rather expensive. Couldn't afford to guess. A precise vacuum easel was mandatory. Now I sometimes work with comparable Fuji Supergloss - easier and cheaper, but not that cheap. More often these days, I make 16X20 fiber-based black and white prints. But even for that kind of application, I'm grateful to have learned how to do things precisely from the very beginning.
 

MattKing

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I agree - seek the highest accuracy your tools can supply.
Can any grain focuser you use give you the ability to see different results with the paper inserted than when it is not?
 

Lachlan Young

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If you can't find the Peak focus finder with the adjustable eyepiece at a reasonable price, Kienzle make a new version of the same device.
 

Andrew O'Neill

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My students have to use the cheapest grain focusers out there... but they're good enough for the 5x7, and 8x10 prints they make... Prints 16x20 and larger really need something like the Peak focuser with the adjustable eyepiece, and that huge mirror. One can easily see way out in the corners. The cheap ones we have are forever breaking...losing parts, etc. The Peak focusers are well machined beauties.
 

DREW WILEY

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Matt, yes, I can see the difference with my Peak paper vs no paper being present. That amount of thickness makes very little difference in the actual print when the lens is stopped down couple of stops, since I focus wide open. But where having very precise focus does in fact play a crucial difference, and where it's very important to have a truly accurate magnifier, is when I make enlarged internegatives or interpositives on pin-registered vac holders, since these in turn are intended for very precise greater enlargements. But the tilting mirror features is one of the best ways to also check critical resolution and alignment way out in the corners of prints of any size - one more reason to buy the Peak Critical unit. I've seen them used as low as $75, though I bought mine new.
The front surface mirrors can be replaced if necessary, but like anything front surface, it must be treated very carefully, so not a realistic option for students. And that's another reason cheap units don't work so well - they use rear-surfaced mirrors which have secondary reflections and aren't generally seated precisely; i.e., they can be somewhat adjusted for central focus alignment, but the glue behind them might make the overall plane behind them irregular. You get what you pay for.
 

MattKing

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The temptation here is really strong to mention that I have thought in the past that Drew sees things that none of the rest of us ever see, but I won't .
I do agree though that the Peak units can be wonderful to work with, and if you have a chance to get one you should.
Another item that is/was really interesting is/was the Hocus Focus, because it also allows one to work right into the corners. Unfortunately it requires one to hold it against the focus surface with one hand, which doesn't suit my needs well.
 

DREW WILEY

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Well, to get the most out of "Peak performance" you need a lens of matching high precision. Not just any enlarging lens will do that, and in the case of internegs and interpositives, I only use Apo Nikkor graphics lenses, which are truly apo in a sense no typical enlarger lens per se is. You can see any potential color fringing right down to the grain size if necessary. Holding it with a hand? Why? Ever heard of the law of gravity? Are you using a vertical wall easel?
 

MattKing

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DREW WILEY

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It doesn't? Mine does. I thought you were referring to "hocus focus" as a pun. You mean there's an actual product called that? I have a real simple solution. Go to Hawaii and catch a few little geckos. Carefully remove the outer layer of skin from their feet, humanely of course. Just lie to them telling them it's a foot massage. Dry this and flatten it in a drymounting press. Find a glue that works in a very thin layer. Add the thickness of it to that of all those little gecko molecular-bonding foot cells, and measured that precisely with a paper micrometer. Apply it to the base of your magnifying device to the effect that it precisely matches your intended printing paper thickness.
Hope that the gecko skin doesn't change color as you apply it, or it might be hard to spot if you drop it. Worse, if it contacts your printing paper, you might end up with gecko foot impression on the print. I haven't actually tried this myself - geckos are just too cute as is - but it seems like a perfectly reasonable solution for someone willing to buy a product with a name like that to begin with!
 

MattKing

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DREW WILEY said:
It doesn't? Mine does. I thought you were referring to "hocus focus" as a pun. You mean there's an actual product called that?
Click to expand...
Yes, or at least there was. It was developed in England and it is intriguing in its simplicity and durability.
And it actually works better than the Peak when it comes to checking focus in the corners of the print, because it is so flexible when you use it there.
But I would prefer a Peak because it is better suited to my circumstances.
And by the way everyone, if you want to do things the way that Drew insists is the only appropriate way, you can always attach a single thickness of photographic paper to the bottom of your magnifier instead of adding paper to the easel.
 

MattKing

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And as for the name, it has been my experience that you are much more likely to encounter a bit of whimsy in a product name from the UK than anything Drew would be likely to recommend, so it doesn't surprise me that Drew (who seems rather un-whimsical at times) doesn't like it .
I expect the product would still be around if Nova Darkroom in the UK hadn't contracted the US distribution rights to JOBO USA, who then went out of business.
I found a really poor internet image of it here, but I doubt you can tell much from it:


It is about 4 inches long in total.
I'll try to retrieve it and post a better image in the next day or so.
Here is another thread about it: https://www.photrio.com/forum/threads/hocus-focus.9684/
I
 

AgX

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Lachlan Young said:
If you can't find the Peak focus finder with the adjustable eyepiece at a reasonable price, Kienzle make a new version of the same device.
Click to expand...
First time I hear this, I do not find it at their website either.
 

Bill Burk

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How can we reconcile that DREW WILEY can see the difference between when paper is inserted versus not, and I can ramp through a tenth of an inch without seeing a difference? I am not talking circle of confusion stuff here. The grain is crisp and sharp across that span.

I will grant that double weight paper calipers at 0.012 inches and that lifts the plane of focus through 12 percent of the 0.099 inches range of sharpness.

And I will grant that I calculate film speed using a graph with divisions of 0.02 (graphs to 0.01 precision by marking lines or the spaces between). And ASA/ISO speeds are rounded to the nearest 0.10 LogE - so the idea of working to mathematical/theoretical precision that exceeds the practical need by a factor of ten is not foreign to me.

So is there a need for you to put double weight paper under a grain magnifier? If you skip the paper, your plane of visible light focus will be low by a tenth of the tolerance.

This error is in the opposite direction and canceled out by another error. Has anyone mentioned the blue filter? Black and white print paper is sensitive to ultraviolet and blue wavelengths which focus in front of green yellow red and infrared wavelengths. So when you use a blue filter you focus more correctly with the grain magnifier than without a filter.

So, use a blue filter on the viewing eyepiece and place a piece of paper underneath to get perfect focus. Or leave off the filter and paper and get the same focus because these two errors cancel each other out.
 

Sirius Glass

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That works until you change to double weight paper. Or a different brand of single weight paper. Just put a sample of what you are working with under the grain focuser. Really, how hard can that be? Just to be sure. Once it become a part of your work flow it is no longer an inconvenience.
 

DREW WILEY

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Need a blue filter? That wouldn't apply well to VC paper, certainly not to color paper, makes viewing dim, and if really needed, implies a funky old enlarging lens poorly corrected, which might shift stopped down anyway, if you even still use graded paper at all, which that antique provision was designed for. Yes, I know that these came as a standard accessory with the better peak magnifiers, so I suppose some kind of excuse has to be made for trying it at least once. Paper rarely sits truly flat anyway unless a vacuum easel is used.
 
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Patrick Robert James

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Well, one of you is full of sheet! I'll let you come to the conclusion which one....
 
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