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Bill Burk
2-Jul-2011, 23:30
I've read that some experiments have shown the plane of sharp focus on the enlarging easel is a half-inch.

So, does that mean I don't need to keep a scrap of enlarging paper to put under the grain focuser?

I've been doing that since I was a teenager and it's hard to break old habits.

But if it's a wasted effort, I may reteach myself to skip it.

Brian C. Miller
2-Jul-2011, 23:45
Why don't you just make a paper step wedge, focus in the middle of it, and observe the results?

Heespharm
3-Jul-2011, 00:06
No not needed but I still do it... I have a sheet of fixed paper used for focusing ... Old habits die hard

Steve Smith
3-Jul-2011, 00:13
We had a discussion on this on APUG last year. I contacted a few manufacturers of grain focusers and the overwhelming conclusion was that it is not required.

Also in his book, The Edge of darkness, Barry Thornton describes how he made a print with a 1/2" board under the easel focused as best he could then made two further prints: one without the board and one with a second board (so 1/2" above and below the original print). He claimed that he could see no difference - and this is from someone who was obsessed with sharpness.


Steve.

davemiller
3-Jul-2011, 00:35
The available depth of field is a factor of the lens focal length and aperture. I suggest that you raise one side of a 16x12 easel by several inches, eyeball focus an image around the centre, and make three large prints, one at maximum aperture, one at minimum and one around the middle of the range and compare them. It is quite easy to get acceptable side to side sharpness in these situations using a small aperture.

ic-racer
3-Jul-2011, 01:09
I've read that some experiments have shown the plane of sharp focus on the enlarging easel is a half-inch.

So, does that mean I don't need to keep a scrap of enlarging paper to put under the grain focuser?

I've been doing that since I was a teenager and it's hard to break old habits.

But if it's a wasted effort, I may reteach myself to skip it.

It depends on the magnification and aperture. You can calculate it with the view camera focusing equation for defocus and diffraction or you can just raise and lower your grain magnifier to see. I can't think of any practical enlarging scenario where the baseboard side depth of field is anywhere near the thickness of a piece of paper.

Elevation changes of the easel are kind of cumbersome. Since many enlargers have a measuring scale on the column, it is easiest to just raise and lower the head to check your focusing depth, and read off the numbers from the column.

As an example a 4x5 negative enlarged to 8x10 at f11 would have about 2.5mm of depth of field at the baseboard.

A Minox negative enlarged to 11x14 at f4 would have about 27mm depth of field at the baseboard.

A piece of paper glued to the bottom of a Peak 1 grain focuser keeps it from scratching one's easel.

tlitody
10-Jul-2011, 10:00
There is a formula (there usually is for theory purposes)

depth of focus at the paper is:

t = 2Nc(1+m)

where t=depth of focus, N=f-number, c= circle of confusion, m=magnification.

circle of confusion on paper needs to give 8lpmm, I used figure for 10lpmm which is 0.05mm

So using above formula and an 8 times enlargement of negative(which is about right for an 8x10 print from 36x24 neg) and f5.6 we get:


t = 2*5.6 * 0.05 (1+8) = 5.04mm

Which means your depth of focus at the paper will be at least 5mm. Putting a piece of paper under the focus finder makes no difference.
And in fact because of the bellows extension the effective aperture f-stop would be around f40 which would make depth of focus around 36mm. And if you are only aiming for 5lpmm then you can double that to around 72mm.

But given that perfect enlarger alignment is unlikely, your margin of error is less than depth of focus might indicate. Good job there is some margin of error cos if there wasn't you'd rarely get an apparently sharp print.
Putting paper under your focus finder won't make any noticeable difference and besides, how do you know the designer did that when they designed it?

p.s. not sure above formula is the most accurate but it should be close enough.

Bill Burk
10-Jul-2011, 12:13
Thanks tlitody and ic-racer,

I think I may forgo the paper. I can use the time I would have spent looking for the scrap of paper to look at the edges to ensure my enlarger is correctly aligned.

Drew Wiley
10-Jul-2011, 13:36
Depends on the depth of field of your enlarger lens, its particular focal length, and how far it is stopped down. Do you defocus your camera shots by half an inch, or
even a millimeter? Why do it on the enlarger?

Bill Burk
10-Jul-2011, 16:02
We're talking about .05 mm thickness of paper.

At the enlarging lens stage or negative stage, .05 mm would be noticeable, but the story I am hearing is that at the paper plane there is more leeway.

Because the subject and sensitive material are arranged differently than in camera, it's like if you are taking a picture of someone and "they" moved a millimeter.

If doing reductions, the sharpness zone is working against me again.

My specifics: D2 enlarger, 135mm Xenar f/4.5 at f/11 - 11x14 from 4x5. I do care about subject sharpness but allow softness at the edges.


Drew, I've got a lot of respect for your opinion - if you say I should keep using paper I will.

Bill

tlitody
10-Jul-2011, 23:37
Depends on the depth of field of your enlarger lens, its particular focal length, and how far it is stopped down. Do you defocus your camera shots by half an inch, or
even a millimeter? Why do it on the enlarger?

Its not depth of field, it's depth of focus at the plane of the projected image. An enlarger is a macro camera. It's taking a picture of the negative. At the negative you have miniscule depth of field. But at the paper you have a much bigger depth of focus, especially when you are enlarging past 1:1. Then the lens extension causes an effective change in the lens aperture. For the parameters given by Bill in last post that would be to around F22 from a set F11.
So using the formula he would get around 8.8mm of depth of focus. (3x enlargement based on 10lpmm). Depth of field at the negative would be about 0.25mm which is why enalrger alignment is much more significant.

Jack Dahlgren
11-Jul-2011, 07:55
We're talking about .05 mm thickness of paper.

At the enlarging lens stage or negative stage, .05 mm would be noticeable, but the story I am hearing is that at the paper plane there is more leeway.

Because the subject and sensitive material are arranged differently than in camera, it's like if you are taking a picture of someone and "they" moved a millimeter.

If doing reductions, the sharpness zone is working against me again.

My specifics: D2 enlarger, 135mm Xenar f/4.5 at f/11 - 11x14 from 4x5. I do care about subject sharpness but allow softness at the edges.


Drew, I've got a lot of respect for your opinion - if you say I should keep using paper I will.

Bill

If you are always using the paper for focusing, consider gluing a bit of it to the bottom of your grain focuser, or tape a flap of it on that you can flip underneath. Best of both worlds.

Drew Wiley
11-Jul-2011, 08:36
OK - I did a misdemeanor on the terminology. Makes little difference. Focus is focus.
Why be sloppy about it? Unless you have a good well-leveled vacuum easel the paper
is going to get a little out of plane. Some papers lie flatter than others. If you start out
somewhat off focus in the first place, it's only going to end up worse where the paper curls. Common sense. It gets even worse with small format when you need to use
wider lens apertures. All this damn math won't change that. It's a lot faster to focus correctly in the first place than to fiddle with an idiotic calculator.

tlitody
11-Jul-2011, 08:59
OK - I did a misdemeanor on the terminology. Makes little difference. Focus is focus.
Why be sloppy about it? Unless you have a good well-leveled vacuum easel the paper
is going to get a little out of plane. Some papers lie flatter than others. If you start out
somewhat off focus in the first place, it's only going to end up worse where the paper curls. Common sense. It gets even worse with small format when you need to use
wider lens apertures. All this damn math won't change that. It's a lot faster to focus correctly in the first place than to fiddle with an idiotic calculator.

Yeah but if the paper curls up and you use paper under the focus finder then you'll make things worse at the edges. Common sense really.:D

The point is, that getting enlarger alignment right is far more significant and if you've done that you don't need to worry about the 0.5mm of a focus finder. And if your enlarger alignment is out your 0.5mm of focus finder height won't fix the problem.

Drew Wiley
11-Jul-2011, 09:56
Agreed. The most important thing is to have everything properly aligned. Having done
this, there are plenty of times I like to optimize the lens performance and focus on a
shallow depth of field to minimize things like dust, anti-newton texture, or even the grain of a secondary masking negative behind the original one. So in certain cases I prefer longer lenses relative to format and relatively wide apertures. For med format I
might even use a 150 Apo-Rodagon wide open at f/4.5, or only a stop down for 4x5.
Sometimes makes a difference with big prints, especially color. Or I might want to fine
tune the degree of falloff by what combination of diffuser, lens, and aperture I choose.
But of course, to do things correctly, there's always some vacuum easels around if
needed. Most of the time for conventional black-and-white printing, they're overkill;
but there have been some instances I regretted not turning on the vacuum.

Bill Burk
11-Jul-2011, 21:32
...But of course, to do things correctly, there's always some vacuum easels around if
needed. Most of the time for conventional black-and-white printing, they're overkill;
but there have been some instances I regretted not turning on the vacuum.

I've grown fond of the squeak of the old bladed easel, and the vacuum will drive the neighbors crazy late at night.

But I've got a vacuum easel I could put to work.

And then I'll have to use a sheet of paper under the focusing scope so it won't scratch the vacuum easel.

At least I don't have to think about whether I'm using single weight or double weight paper.

Steve Smith
12-Jul-2011, 00:15
If you are always using the paper for focusing, consider gluing a bit of it to the bottom of your grain focuser, or tape a flap of it on that you can flip underneath. Best of both worlds.

Don't bother. We had a discussion about paper under grain focusers on APUG last year. I contacted and got replies from a few manufacturers. The concensus was that you do not need to put paper under it as there is no point. My view is that the manufacturer probably compensates for the paper anyway so putting paper under it puts it too high but either way the depth of focus makes the paper superfluous.

Do it if it makes you feel better but it doesn't really make any difference.

EDIT: Looks like I already mentioned this at the start of this thread!!


Steve.

Drew Wiley
12-Jul-2011, 08:21
How does the mfg of a magnifier compensate for the thickness of paper when this
thickness is not standardized? I have a top of the line Peak magnifier, same mfg as my
optometrist uses for his equipment. I'm sure glad they didn't operate on the assumption
that eyeryone's eyeballs are exactly the same. I also use this magnifier for very critical
work like enlarged interpositives and internegs, and it certainly isn't skewed for the
thickness of anything.

Drew Wiley
12-Jul-2011, 08:53
I probably should have qualified my last remark. In the past quite a few El Cheapo
enlarging magnifiers were made, and it probably wouldn't make a hill of beans of difference if you put paper under them or not, because the quality control of the equip
wasn't that good to begin with. Common sense. But with the better units, like the Peak
Critical Focus magnifier, which typically have front surface mirrors and tight tolerances,
it will make a difference for fussy work. The added advantage of this kind of magnifier
is that you can view the corners of the projected image and not just the central area.

Steve Smith
12-Jul-2011, 11:15
This is the reply I got from Tohkai, manufacturer of the Peak focuser:


At first, it is not necessary for you to place a piece of paper under the focuser, but at the same time this is not compensated for in the desing. Because we conshider that the differnce from the thickness of a paper is the tolerance. In face, we have never heard from our customers about any inconvenience from that tolerance

So yes, I am wrong about the manufacturers compensating for the thickness but this is irrelevant as it doesn't really matter.

I had this reply from Roger Parry at Patterson:


Hi Steve, There is no need to put a piece of paper under the focus finder.

I later asked Roger if this was due to paper thickness being designed into the device and this was his reply:


Hi Steve
I was not around in the company when the focus finders were designed but from my own experience the finders work perfectly without a sheet of paper under them. In fact a sheet of processed and dried paper will be different from an unprocessed sheet and you would not want to waste a second sheet of paper on every print you make.

(not sure why you would waste a fresh piece of paper each time though!).


Just to show that there is some confusion, Lisa Weingarten from Magna-sight said:


Hi, I always have a scrap paper under the Magna Sight of the same weight of paper that you will be printing on.


Also, In his book 'Photographic Printing' Gene Nocon regards using a piece of paper under the focuser as a waste of time.

He's a much better printer than I will ever be so I have always followed this advice.


Steve.

Steve Smith
12-Jul-2011, 11:24
How does the mfg of a magnifier compensate for the thickness of paper when this thickness is not standardized?

I think the answer which I quoted from Peak (in my previous post) sums this up. They consider the paper thickness to be more or less equal to the manufacturing tolerances in the unit itself.


Steve.

Jon Shiu
12-Jul-2011, 13:26
Also outside the bounds of repeatability of the user's focus adjustment.

tlitody
12-Jul-2011, 14:07
How does the mfg of a magnifier compensate for the thickness of paper when this
thickness is not standardized? I have a top of the line Peak magnifier, same mfg as my
optometrist uses for his equipment. I'm sure glad they didn't operate on the assumption
that eyeryone's eyeballs are exactly the same. I also use this magnifier for very critical
work like enlarged interpositives and internegs, and it certainly isn't skewed for the
thickness of anything.

I have a top of the line peak too and its no better than my very cheap paterson finder. Infact the paterson is easy to focus and stays in focus. The peak goes out of focus every time you touch the focus ring. The only advantage of a peak is that you can see into the corners. And how do you know you've focussed the peak properly, it doesn't snap into focus in the way a cheap paterson does.

Steve Smith
12-Jul-2011, 14:39
Also outside the bounds of repeatability of the user's focus adjustment.

Indeed. How many degrees of rotation of the focus knob translate to the thickness of the paper in focus position? It's more likely to be measured in minutes rather than degrees.


Steve.

Drew Wiley
12-Jul-2011, 15:26
I don't know what the heck model of Peak or whatever you've got in mind. Mine is built
like a little tank and holds focus perfectly. I've tested its accuracy with some very finicky enlargements on film etc, not just paper, and specifically cases where the difference in paper or even film thickness would be a make or break quality distinction. There is a separate reticle focus within the eyepiece to make sure you've got it properly set. A very precise instrument. There is even a separate blue glass filter just in case you're not using an apo corrected enlarging lens.

Steve Smith
12-Jul-2011, 22:29
There is even a separate blue glass filter just in case you're not using an apo corrected enlarging lens.

Gene Nocon suggests that the use of the blue filter will make a lot more difference than putting a piece of paper under it.


and specifically cases where the difference in paper or even film thickness would be a make or break quality distinction.

The film flatness and position relative to the lens is much more critical than the paper to lens distance.


Steve.

Drew Wiley
13-Jul-2011, 10:11
I've found the blue filter to be relatively useless with modern enlarging lenses which are
well corrected, and obviously of no value with my true apo process lenses. Some time ago I horse-traded for a bunch of drkrm equip which included some old style Componon lenses, where a blue filter might have helped with graded papers; but
I didn't keep any of these old lenses.

cyrus
13-Jul-2011, 10:20
I have and use a Peak focuser too. Certainly, the old trusty Paterson did just fine, but it couldn't get into the corners as well. I needed that for alignment-checking and for large prints. Like many things in a darkroom, it isn't a "must have" but is a "good to have."