Focusing t-grain vs. traditional grain negatives

hpulley · Dec 13, 2010

Where do you focus with t-grain films? Not sure if this is a question for this subforum or the B&W film and paper group but here goes:

I used to print ages ago but back then I never used t-grain films, just traditional ones. Now I've been shooting some of both, HP5+ and FP4+ which I always used and enjoyed and some Delta of various speeds as well. Since the time when I used to do darkroom before I mostly had others do the dev and printing so I didn't look for this but now that I'm doing both myself again I guess I'm finally paying attention and I noticed that e.g. HP5+ has a flat 2-D grain structure while the Delta 400 and 3200 films have a deeper 3-D structure. Delta 100 is fairly tight and the grain is very small anyways so this is more a question about the fast films.

Back to my question, with HP5+ it is obvious where to focus using the grain 'scope, as you move the focus the whole 2-D structure comes into focus essentially at once. With the fast Delta films instead there is a 3-D lattice which comes into focus. Do I aim for the middle of this, the top, the bottom? Does it really matter if I'm going to stop the El-Nikkor down to f/8 anyways?

Ian C · Dec 13, 2010

Focusing at Selective Depths in a Film Emulsion

This doesnt make sense in my experience. Modern film emulsions are extremely thin. This article puts it at less than .001 (.0254mm) thick.

http://electronics.howstuffworks.com/film3.htm

Its inconceivable that you, I, or anyone could perceive focus at various depths of the emulsion with a typical 2-element 20X grain focuser. If the grain structure at any depth is in focus, then so too is all of it.

Even if this were the case, how could the focusing mechanism of an enlarger be moved in small enough increments to alter focus selectively from one depth of the emulsion to another? Can you alter the lens to negative distance in .0005 (0.0127mm) increments or finer? I dont think its possible with the focusing mechanisms enlargers are equipped with.

To discern the grains at various depths in the emulsion would require a very powerful microscopemore likely an electron microscope.

Its usually much easier to focus by closing the lens to the working aperture to grain focus. This makes the grain much more well-defined and seems to have better contrast than trying to focus with the lenss aperture wide open. Its also much more comfortable to the eye, since the bright light will be reduced to 1/4th its original intensity by stopping down 2 stops.

Ive used many types of films since 1985. I havent noticed any difference in how I perceive the grain as I refine the focus, only differences in grain size and pattern.

hpulley · Dec 13, 2010

Thanks for your reply.

I'm just reporting what I see which is that there are layers of grain in the Delta 400 and 3200 films, it is obviously deeper in structure than HP5+. Perhaps I'm not knowing what I'm looking about but with the old coarse knob on the Durst M-300 with 50mm f/2.8 El Nikkor this is what I see... I find it easier to find precise focus at f/2.8, at smaller aperture the depth of field makes it looks in focus over a wider range.

ic-racer · Dec 13, 2010

Focus on the "far" grain structure, then move the enlarger head up to get the "near" grain structure in focus. The change in distance on the enlarger column between the two head heights can be used to calculate the actual depth of what you are seeing by using the simple lens equation:

1/f = 1/p1 + 1/q1
1/f = 1/p2 + 1/q2
with emulsion depth = p1-p2

Where:
f = focal length of enlarging lens
p1 = near distance from lens to baseboard
p2 = far distance from lens to baseboard
q1 = distance from lens to top of emulsion
q2 = distance from lens to bottom of emulsion
q1-q2 = depth of emulsion

hpulley · Dec 13, 2010

Thanks for the equations. I'm not sure that there is enough movement in between for me to get a measurable distance with the tools I have but I'll see what I can do.

Jerevan · Dec 13, 2010

Ic-racer,

do you see the same thing as hpulley does? You must be doing serious enlargments or use pretty some high-res grain focus. I've never seen anything except that it is really hard to find the grain on T-grain films.

hpulley · Dec 13, 2010

Jerevan said:
Ic-racer,

do you see the same thing as hpulley does? You must be doing serious enlargments or use pretty some high-res grain focus. I've never seen anything except that it is really hard to find the grain on T-grain films.

You're shooting 35mm Delta 400 and 3200? Enlarging to 11x14"? Am I crazy? Perhaps I don't want an answer to that one but I see what I see, not sure these eyes are shot. Perhaps I can project the image, hook my macro lens and Bellows FL up to a camera and take a picture of the grain at near, middle and far focus so you people believe me.

Jerevan · Dec 13, 2010

Okay, I have only done Tmax 100 (and Ilford 3200 but that was so long ago that I can't be held responsible for it!) so I am just interested in what you are able to see. And no, you're not totally crazy - I've done close to 11x14" with HP5+.

Nicholas Lindan · Dec 13, 2010

What you are seeing are diffraction patterns on either side of the actual focus point. They are an artifact of the interaction of the film, the enlarging lens, the grain magnifier, eyeglasses or contacts and your eyes.

If you are focusing with eyeglasses on try taking them off - you may have to refocus the magnifier.

If you are stopping down to f8 I wouldn't worry too much - the only meaningful test is to ask "Are the prints sharp?"

I find I can focus just as accurately without a grain magnifier as with - a benefit of horrid nearsightedness.

Allen Friday · Dec 13, 2010

Why not make two prints and compare the results? Print one, focus on the near edge. Print two, focus on the far edge. Process both and compare the results.

hpulley · Dec 13, 2010

With my sharpest lenses I love the results of HP5+ at 11x14" (actual image size less than 11x14" obviously due to the easel blades). Souped in DD-X the prints show almost no grain at that size when exposed and developed correctly. Surprisingly good.

I do wear eyeglasses. I didn't think to try without them.

I too find I can focus very well without the magnifier though I guess I don't trust myself that well yet. I also wondered if I should focus differently for RC or DW fiber since the paper thickness is different. So far I've used the correct dummy paper in the easel, refocusing when I switch but perhaps I'm being silly.

Doing two test prints is of course the obvious answer though if I'm really just confused by diffraction patterns then it would be a waste of paper, though not much more than my usual printing workflow LOL

Steve Smith · Dec 13, 2010

You are more likely to be seeing the two extremes of depth of field. Although it will be small with the aperture wide open, it will still be larger than the emulsion thickness.

Steve.

Steve Smith · Dec 13, 2010

hpulley said:
I too find I can focus very well without the magnifier though I guess I don't trust myself that well yet. I also wondered if I should focus differently for RC or DW fiber since the paper thickness is different. So far I've used the correct dummy paper in the easel, refocusing when I switch but perhaps I'm being silly.

The paper/emulsion thickness is largely irrelevant. We had a thread about this last year. I suggested that paper in the easel was not necessary as I thought the manufacturer would compensate for it. I contacted three focusing aid manufacturers and two of them responded that putting paper in the easel was not necessary.

With that in mind, the emulsion and/or paper thickness will not make much difference.

In his book Edge of Darkness, Barry Thornton (a confirmed sharpness freak) did a test. He put a 1/2" piece of board under his easel, focused and made a print. He then made two more prints, one with an extra board and one without the board (so 1/2" either way of focused). He claimed that he could see no difference.

Also Gene Nocon in his book Darkroom Printing says not to bother with the paper.

The relationship between the negative and the lens is much more important than that of the lens to the paper.

Steve.

ic-racer · Dec 13, 2010

Jerevan said:
Ic-racer,

do you see the same thing as hpulley does? You must be doing serious enlargments or use pretty some high-res grain focus. I've never seen anything except that it is really hard to find the grain on T-grain films.

No, just pointing out the equation

hpulley · Dec 13, 2010

Thanks everyone. Seems I'm worrying about nothing. My 11x14" easel has a yellow backing so I find it easier to see things with a white piece of paper in place so I'll continue to use it but it seems I need not bother worrying about DW or RC paper.

dpurdy · Dec 13, 2010

I actually have seen the same thing or something like it hpulley. On some film, maybe mostly acros, it seems there is something else that can come into focus just off the grain. I was thinking it was perhaps something in the film base. I don't worry about it and I always stop down a couple stops anyway. Best to find something in the image that is sharp to include in what you are looking at in the grain focuser.
Dennis

paul ron · Dec 13, 2010

Opem the lens all the way when focusing so you don't have the DOF of the lens giving you aymore depth than the thin emulsion itself so you can focus faster n more critical.

declark · Dec 13, 2010

Steve Smith said:
In his book Edge of Darkness, Barry Thornton (a confirmed sharpness freak) did a test. He put a 1/2" piece of board under his easel, focused and made a print. He then made two more prints, one with an extra board and one without the board (so 1/2" either way of focused). He claimed that he could see no difference.

So if a 1/2" one way or the other doesn't make a difference why even bother with a grain focuser? I can easily guess within a 1/2" head height?

hpulley · Dec 13, 2010

It makes sense in some ways, you can tilt the head and/or the easel to fix keystoning and that obviously needs some depth of field for it to work but you're right, it does make you wonder why bother with a grain magnifier at all.

MattKing · Dec 13, 2010

I find that the grain magnifier makes it easier to see the grain, so I use it.

As others have said, for 11x14 enlargements, if you think you are observing "depth" in the emulsion, you are mistaken. Any depth you see relates to something outside the emulsion layer.

Steve Smith · Dec 13, 2010

declark said:
So if a 1/2" one way or the other doesn't make a difference why even bother with a grain focuser? I can easily guess within a 1/2" head height?

Because you still have to get it in focus. It's just that the depth of focus is greater than you might think it is.

And that depth of focus can change quite a bit with a very small lens to negative movement.

Most people focus by moving the focusing knob both directions so you find the two points at which the image starts to go out of focus and then you end up with it in a middle position (hopefully). In this position the paper is in the middle of the depth of focus and a bit of movement up or down will not be noticeable.

Steve.

cowanw · Dec 13, 2010

What ever it is you are not alone, hpulley. I would have sworn the same thing.

declark · Dec 14, 2010

Thanks for clearing that up Steve. It's been a few months since I printed anything and now I see what you are saying. Once it is in focus, a slight change in the head height probably doesn't alter sharpness much, just the projected image size.

Steve Smith · Dec 14, 2010

The enlarger is really a macro camera with huge magnification. The negative is the subject and the paper takes the place of the film. As anyone who has done any macro work will know, there is hardly any depth of field on the subject especially when you go to magnification greater than 1:1. With an enlarger this translates to depth of field around the negative which is why negative flatness is important and why some people use glass negative holders despite the extra surfaces which need to be kept clean.

Steve.

hpulley · Dec 15, 2010

OK so I tried it with and without my glasses and I think it is my glasses that are causing the problem. This is a bit odd however as I often use glasses with my telescope and I would have thought the small exit pupil would give similar problems but I guess the objects near infinity are very different from this case where the object is at minimum focus distance.

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