Using grains focuser with or without paper on the easel

MattKing · Jun 22, 2021

Those are different DOF numbers than the ones I "calculate" for 1/8 life-size I get ~35 mm of depth of field for that magnification.
Are you sure your number isn't for a magnification of 8x? rather than 1/8x?
Disclosure - I just went to this online DOF calculator, rather than doing the hard work: https://www.photopills.com/calculators/dof-macro

wiltw · Jun 22, 2021

MattKing said:
Those are different DOF numbers than the ones I "calculate" for 1/8 life-size I get ~35 mm of depth of field for that magnification.
Are you sure your number isn't for a magnification of 8x? rather than 1/8x?
Disclosure - I just went to this online DOF calculator, rather than doing the hard work: https://www.photopills.com/calculators/dof-macro

I used this macro DOF calculator, https://www.kielia.de/photography/calculator/
I did another calculation and used 50mm lens (same as enlarging lens for 135 format) at f/8, I assumed a 0.51m focus distance, which resulted in 1:8.1 scale shot or 0.12x
Calculated DOF zone (assuming 20/60 vision manufacturer standard) from 0.491m to 0.530m

AgX · Jun 22, 2021

But even if we want to focus precicely by using a grain focuser and preassuming that

-) the plane of focus (made out of flatness of the negative and the flatness of the focal plane of the lens itself is beyonf the the thickness of that paper
-) that the grain focuser even in itself is adjusted beyond the thickness of that paper
-) that the plane over the four edges of the baseboard is perpendicular to the optical axis beyond an angle that yield lesser height deviation than the thickness of that paper
-) that the paper lies everywhere in contact with the baseboard (maybe by vacuum)

then still remains the issue of the flatness of the baseboard.
I got a 60 years old baseboard made from plywood or carpenter's board. And even modern MDF boards are not ideally flat...

MattKing · Jun 22, 2021

wiltw said:
Calculated DOF zone (assuming 20/60 vision manufacturer standard) from 0.491m to 0.530m

Those are meters, not millimeters.
Works out to 39 millimeters depth of field.
If you adjust the circle of confusion down to 0.009 mm (for 20/20 vision) the depth of field goes from 0.495m through 0.505m or 10 millimeters.
Still pretty deep, compared to the thickness of a sheet of photographic paper.

Lachlan Young · Jun 22, 2021

AgX said:
then still remains the issue of the flatness of the baseboard.
I got a 60 years old baseboard made from plywood or carpenter's board. And even modern MDF boards are not ideally flat...

Exactly. And how many baseboards/ easels have a runout less than the thickness of a sheet of average darkroom paper (or film for that matter)? Even vacuum easels (while accurate enough) were never made as surface plates for the large part (there may have been some for extremely arcane applications in cartography or metrology).

cliveh · Jun 22, 2021

When using an enlarger it is not depth of field, but depth of focus. Depth of field is a camera function. Well in the UK it is.

faberryman · Jun 22, 2021

MattKing said:
Those are meters, not millimeters.
Works out to 39 millimeters depth of field.
If you adjust the circle of confusion down to 0.009 mm (for 20/20 vision) the depth of field goes from 0.495m through 0.505m or 10 millimeters.
Still pretty deep, compared to the thickness of a sheet of photographic paper.

Wow! When you put it that way, why bother with a grain focuser? F/8 and be there.

Mainecoonmaniac · Jun 22, 2021

I am not too concerned about depth of field on focusing my easel, I tend to use f8 because that’s the sharpest aperture from years of experience.

Luckless · Jun 22, 2021

cliveh said:
When using an enlarger it is not depth of field, but depth of focus. Depth of field is a camera function. Well in the UK it is.

An enlarger is just kind of an inside out camera, with the subject and light in a smaller box that is positioned inside the bigger light tight box that the recording medium is setup in, so what exactly is the difference between 'depth of field' and 'depth of focus'?

MattKing · Jun 22, 2021

faberryman said:
Wow! When you put it that way, why bother with a grain focuser? F/8 and be there.

Au contraire!
Near the paper, the position of the focus magnifier doesn't matter much. Anything reasonably close will give good results.
Near the lens, the position of the negative matters a lot. Anything even slightly off will give bad results.
And when you change that negative position a bit, the magnification changes quite a bit.
This is why auto-focus enlargers are both as convenient as they are and reasonably accurate, even when the "fine focus" adjustment (if there is one) isn't employed.

MattKing · Jun 22, 2021

cliveh said:
When using an enlarger it is not depth of field, but depth of focus. Depth of field is a camera function. Well in the UK it is.

Luckless said:
An enlarger is just kind of an inside out camera, with the subject and light in a smaller box that is positioned inside the bigger light tight box that the recording medium is setup in, so what exactly is the difference between 'depth of field' and 'depth of focus'?

And if you reference some of the more detailed Kodak reference materials on close focus and macro photography, they add another term - depth of subject.
I believe that Clive is correct, but I find that if I use depth of focus in relation to either enlarging or projecting (where it also applies) many respond with quizzical looks.

Don_ih · Jun 22, 2021

Anyone here who cares has both an enlarger and a grain focuser. Soooooooo...., just go check for yourself. At any rate, this continues to be something that no one should argue about.

MattKing · Jun 22, 2021

Don Heisz said:
At any rate, this continues to be something that no one should argue about.

Probably not.
However I do think that thinking about how this stuff works improves my understanding of how to get the best out of the darkroom equipment I use.

wiltw · Jun 22, 2021

Luckless said:
An enlarger is just kind of an inside out camera, with the subject and light in a smaller box that is positioned inside the bigger light tight box that the recording medium is setup in, so what exactly is the difference between 'depth of field' and 'depth of focus'?

I see strong parallels between an enlarger projecting image on paper in easel, and camera taking a photo of flat art.

There is Depth of Focus pertaining to the neg in the neg carrier of the enlarger and to the film in the camera
There is Depth of Field pertaining to the paper on the easel and to the flat art being photographed
There are great parallels between the enlarger lens and the flat field corrected lens on the camera.

Arguably one might say the enlarger has Depth of Focus at both sides of the lens, although much written on the topic says Depth of Field applies 'in front of the lens' and Depth of Focus applies 'behind the lens', but we do not generally see such discussions in the context of enlarging.

warden · Jun 22, 2021

Bill Burk said:
Has anyone measured the depth of sharp focus? This is a test I have performed and it convinced me the critical depth nears 1/10 inch. Put a significant slant to your easel. For example raise one side an inch. Put the grain focuser on the easel and focus on a negative. Observe as you slide the focuser up and down slope to find the “just noticeable difference”. Measure this distance you slide and triangulate to find the critical depth.

When I got my first enlarger as a complete beginner maybe 10 years ago I bought a good grain focuser and one of those laser tools that makes sure the easel is exactly parallel with the enlarger lens. (It's a neat toy, btw, that probably nobody needs.)

Anyway, I had a negative that needed quite a lot of perspective correction so I tried tilting the easel, quite a bit actually, by stacking a fist-full of quarters under one edge of the easel, and the whole image was still in focus! It was surprising to me how much depth of field I had to work with, and of course that made me realize that using a piece of paper under the grain focuser wasn't really helping anything other than making it easy for my awful eyes to focus the lens. So I still use the bright paper because it helps me see, but I know it's not critical to focus the grain.

Sirius Glass · Jun 22, 2021

MattKing said:
This would be true if it was actually possible to see the difference when you are viewing the enlarged grain with the focuser.

It is true even if you cannot see the difference. The fact does not change. It makes sense to keep in the middle of the focus range and not risk any focusing problems.

wiltw · Jun 22, 2021

Sirius Glass said:
It is true even if you cannot see the difference. The fact does not change. It makes sense to keep in the middle of the focus range and not risk any focusing problems.

^
We strive for 'perfect focus' when we are shooting a photo of flat art, so why be any more casual minded or sloppy when projecting that same neg onto enlarging paper? It is a matter of principle, not an exercise of 'what can I get away with in sloppiness?'
There are lots of places where sloppiness is inherent, and we get away with it...

is the aperture truly f/4 or is its diameter really f/3.9 or f/4.2.
are we really getting 1/500 out of that leaf shutter?

Sirius Glass · Jun 22, 2021

wiltw said:
^
We strive for 'perfect focus' when we are shooting a photo of flat art, so why be any more casual minded or sloppy when projecting that same neg onto enlarging paper?

Finally someone gets it. Thank you. Those that refuse to take all the measures possible to get the best out of the negative are deserve whatever they get.

DREW WILEY · Jun 22, 2021

There are several relevant factors. Not all grain magnifiers are created equal. I've seen cheaper ones shimmed or padded at the base with material which swells or contracts in thickness with humidity changes. If you have a serious quality magnifier on hand like a Peak Critical Focus magnifier on hand for sake of comparison, you might discover just how far off certain others can be. Most enlarging easels are not dead flat, nor will FB paper lie truly flat in them without a vacuum option. Sone have bumpers on the bottom of them that differ slightly in height. Papers differ a little in thickness (generally a minor issue). Short focal length enlarging lenses have less focal plane tolerance than longer ones. The specific f-stop in use also matters. And of course, never take it for granted that your plane of focus in the carrier is perfectly level and flat with respect to your baseboard plane itself (if it is even truly flat). Some enlargers might tend to skew in this respect at different height positions - the column itself is not consistent or a precise fit to the carriage. Everything needs to be checked first, once you set up an enlarger and get an easel.

Bill Burk · Jun 22, 2021

Oh I put paper on my easel to compose, but haven’t put paper under my grain focuser for years. I was convinced by somebody here.

It would depend on the enlargement, I alike the analogy of Macro.

Focus a 35mm macro at 1:10 and aim at a ruler held at 45 degree angle. What’s the range of sharp image according to what looks clear and crisp in the microprism?

It is near an inch to unaided eye, I suppose I might find it significantly less using focus magnifier. But still probably a half inch there.

Dirb9 · Jun 22, 2021

If we're being really pedantic, you don't want your plane of focus on the surface of the paper anyways, as most modern papers have surface coat(s) above the emulsion layers. I'm aware of at least a few camera manufacturers that specify somewhere in their service manuals that the back focus distance should be measured and adjusted to be within the emulsion itself, not the surface of the film, for the same reason.

Or, as other people have opined, there are so many other factors that have larger effects on the final print that the whether or not the paper is present for focusing is irrelevant.

DonW · Jun 22, 2021

More time spent learning how to take outstanding photographs and less time delving into matters that might only effect the finished product by maybe less than .01% is a better use of your time.

Don't believe me? Check out HCB's famous images. Many are out of focus.

MattKing · Jun 23, 2021

Sirius Glass said:
It is true even if you cannot see the difference. The fact does not change. It makes sense to keep in the middle of the focus range and not risk any focusing problems.

You miss the significance.
If the instrument you use to determine whether or not something is at a position of best focus is your sight, than if you cannot differentiate between the accuracy of two positions with that sight, then it doesn't matter which of the two positions you choose - each will be equally likely to be the best choice.
And your sight will not be capable of telling which of the two options will be best, because of how all of this particular optical system works.

reddesert · Jun 23, 2021

When attempting to control a process, it's important to understand what really makes a significant effect and focus (haha) your efforts on that. Several people have already pointed out that enlarger alignment and negative flatness - which must be within the depth of focus at the negative - are much more sensitive than depth of field at the paper.

Of course, it doesn't take much effort to put paper under the grain focuser, so you might as well do it. But all the mental effort spent fussing about it could be better spent on testing whether your enlarger is aligned or if you are stopping down the lens enough to cover negative flatness, for example.

Don_ih · Jun 23, 2021

MattKing said:
However I do think that thinking about how this stuff works improves my understanding of how to get the best out of the darkroom equipment I use.

That is true. My only real point is people should check for themselves before being dogmatic one way or the other.

The most important part of using a grain focuser is making sure the enlarger lens is wide open when you use it. And then the larger the aperture of the lens, the tighter the focus. Maybe at f1, the thickness of the paper would actually matter, but who would make an enlargement at f1?

DonW said:
Check out HCB's famous images. Many are out of focus.

He didn't enlarge them, though. If he had, they probably would've been even more blurry.

Using grains focuser with or without paper on the easel

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