I've noticed that when printing on large paper sizes (8x10, 11x14, and larger) the paper doesn't lay very flat in the easel. I know that there are expensive vacuum easels to ensure sharpness by hoding the paper flat, but I was wondering if by stopping down the enlarger lens (f11 or f16 or so) that would give the extra DOF to help counter any slight curves or bulges in the paper. Additionally, by using a smaller aperture help counteract slight mis-alignments in the carrier and baseboard/easel? Similarly, when the film isn't flat in the carrier, would a smaller aperture help as well?

-- Scott Flathouse (seflathouse.pampa@celanese.com), May 10, 2000

Answers

Yes to all your points: stopping down will give you the depth of field you need on the easel and in the negative holder. Frankly, I prefer printing at f/11 or f/16, as it gives time to dodge, and allows for finer time-adjustments. Others have described distortions (diffraction) resulting from lens apertures that are too small, but I have not detected that problem in my work.

-- Sam (sselkind@home.com), May 10, 2000.

I only use f8 or f11 when printing.What type of easel are you using. I'm using a Saunders 4 blade model, it hold 11x14 dw fiber paper very flat.

-- Robert Orofino (rorofino@iopener.net), May 10, 2000.

My guess is you must be using a plastic masking frame (easel) with hardly any weight to it, or storing your paper badly, so that it curls up. Every metal masking frame I've used, even the cheapest, has held the paper flat, and I think I've used every major brand from Gnome (now defunct) through to J J Beard. The major difference between the cheaper ones like LPL and expensive ones like Beard is how smoothly they work, and how long they'll last.

-- Pete Andrews (p.l.andrews@bham.ac.uk), May 11, 2000.

Stopping down does increase your DOF, but it also reduces overall image sharpness due to diffraction. Every lens has an optimum aperture, usually between 1 1/2 and 2 1/2 stops down from max. aperture. DOF grows as the distance between the negative and the paper grows, so for big prints, there is already some DOF w/o your having to stop down further.

Sharpness aside, I would see distortion as a much more critical problem, if your subject contains geometrical shapes with straight borderlines. Distortion is also a compelling reason why you should strive for proper alignment.

I had the same problem with some FB papers, and I solved it by using a sheet of glass from a frameless picture holder to hold the paper down. A good sheet of glass is probably much cheaper than an easel, and it works fine. All you have to do is keep the glass clean.

Oh yes: Don't use anti-reflex glass for this!

-- Thomas Wollstein (thomas_wollstein@web.de), May 11, 2000.

I'm using a Bogen 11x14 2-bladed metal easel, and I store my paper in the original boxes in the black plastic sleves. However, there still appears to be slight waves and bulges in the paper as it lays on the easel. Perhaps air trapped underneath it?

For MF work, I use a Nikkor 80mm 5.6, and I usually stop down to f11, which puts the lens in what should be considered the "optimum" aperture of a couple of stops closed. I haven't noticed a major problem with sharpness, and I figured that I could attribute that to the DOF. However, I still would like to eliminate as much as possible any sources of error, and paper flatness seemed particularly irksome.

I'll have to try the sheet of glass to see if I can notice a difference, that sounds like a great tip.

-- Scott Flathouse (seflathouse.pampa@celanese.com), May 11, 2000.

You know...everything was okay until that sheet of glass bit. You will probably never see a probelm with paper flatness unless it is really curled. Even the cheap Speedeasels are fine. But, glass between the enlarger lens and the paper could be the worst probelm found. Glass bends light at its surfaces. If you are doing good without the glass, why put something else in there? You cannot add a glass filter to an enlarger lens due to the bending of light through the glass, so why add glass further down? In other words, after a lens has formed an image, you can't pass that image through glass without a problem. That is why printing filters, and behind-the-lens LF filters, are always gel. The random light going into a lens is okay through glass, but not the image forming out the other side. I tried to use deep green and deep blue camera filters for split printing once, and discovered the hard way what happens "behind" (or under)the lens. I used to print on an old 8x10 enlarger with a 300mm Nikkor. It was amazing how much DOF change was visible with that lens. Try focusing off a little bit wide open, then just watch as you stop the lens down a bit. We don't do that normally in the darkroom, so we forget it works the same as a camera.

-- E.L. (elperdido65@hotmail.com), May 11, 2000.

The Lost One (E.L.)

>You will probably never see a probelm with paper flatness unless it is really curled.<

Just what does "really curled" mean? "Really curled" is when the problems begin. In fact, some FB papers are "really curled", at least to the point of causing distortions. Not all of us have the chance to store their papers under optimum conditions.

>glass between the enlarger lens and the paper could be the worst probelm found.<

Could be, but needn't be. If the paper curls, and the glass is proven to be OK, the glass is the better choice. That is why you should use glass of good quality.

>You cannot add a glass filter to an enlarger lens due to the bending of light through the glass, so why add glass further down?<

Glass further down doesn't make as much of a difference. The problem with deflections of the light rays by glass becomes really bad when the deflected rays still have a long way to travel. Then the slight angular deflection results in a large deviation. "Long" in this context means that the order of magnitude of the distance travelled through the glass gets close to that of the distance between the lens plane and the plane of focus.

>In other words, after a lens has formed an image, you can't pass that image through glass without a problem. That is why printing filters, and behind-the-lens LF filters, are always gel. The random light going into a lens is okay through glass, but not the image forming out the other side.<

You can reverse every light ray without violating the laws of optics. You won't have much of a problem with filters between the lens and the image if you focus that image with the filter in place.

>It was amazing how much DOF change was visible with that lens. Try focusing off a little bit wide open, then just watch as you stop the lens down a bit. We don't do that normally in the darkroom, so we forget it works the same as a camera.<

I don't understand how the DOF should change. What does change (and the long lens with its small DOF lets you clearly see it) is the plane of focus. If you focus an image and then insert something with parallel boundary surfaces between the lens and the image (say an optical cell with a medium whose diffraction number is different from that of air) you will still get a sharp image, but at a different distance from the lens! Impurities scattering the light aside, the image sharpness will be as good as before. The difference in focal length is the greater the longer the distance travelled through the medium in the cell. That's why one should use thin sheets of glass.

-- Thomas Wollstein (thomas_wollstein@web.de), May 12, 2000.

BTW: I forgot to mention the interesting observation by Ctein who found that the effect of below-the-lens MG filters on image sharpness was (and he was surprised to find that) barely noticeable, if anything.

-- Thomas Wollstein (thomas_wollstein@web.de), May 12, 2000.

And Ctein found that the optimum aperture for enlarging lenses is much more wide open than most people think. Like in the f4 range.

-- Terry Carraway (TCarraway@compuserve.com), May 12, 2000.

Here's a trick I learned before I purchased a 16x20 easel. Take out about 10-15 sheets of fibre paper. Then place each two sheets with emulsion side in contact(i.e.,flip every other sheet). Place them in a black 16x20 bag and then place a heavy weight on the stack, such as a 50 sheet box of 16x20. Leave for a couple of days and at your next printing session you will have very flat paper. Also works for smaller sizes.

-- Gene Crumpler (nikonguy@worldnet.att.net), May 15, 2000.

Scott, lots of good advice here. Let me add a couple. Always print one size smaller(i.e 11x on 16x paper)... or print smaller, "odd" sizes on standard paper sizes. What I'm saying is leave room. Room for linen tape and edge damages and most importantly room for the curl. A four bladed easel should hold all but maybe a little of the edges flat so print just inside that curl. What might also help is buy single weight to 11x14...and double weight above that dimen. I've noticed that double-weight 8x's almost never get flat before or after. And it's mfg to mfg on 11x's. Good luck and I hope this made sense.

-- Trib (linhof6@hotmail.com), May 17, 2000.

If you are using a metal easel with metal blades, just put some magnets on the blades once the paper is in place.

-- Alan Shapiro (ashapiro@yorku.ca), May 18, 2000.