Keeping paper flat on exposure

I am printing on ILFORD RC papers and none of the easels I tried seems to hold it flat enough. Things get only worse as paper format gets larger. Results are still good, but I believe flattening the paper would make images even sharper.

 

So I am considering buying a vacuum plate. Some really large plates - up to 25 inches - are available at relatively decent cost of 100-250$.

 

Does anyone have experience using such devices in the darkroom? Are there any concerns? I could imagine only tiny vacuum force would be needed to keep paper flat...no need for tons of forces :)

 

Would appreciate any other tricks on how to keep paper flat :)

What kinds of easels have you tried? I have used Saunders 4 blade easels and they do a good job of holding RC as well as fiber base papers flat. Borderless easels never seemed to work for me and I stopped using them.

I never had problems keeping up to 8x10 flat with the usual easels.

 

I only rarely have done 11x14, and also don't remember it being hard to keep flat.

 

If you want borderless, though, the vacuum easels are probably the way to go.

Pressed enter too early.

The issue seems to be not that much in easel, but in that ILFORD RC multigrade papers are really curved, especially when fresh. I had some old stock ILFORD fixed contrast papers which are dead flat, probably due to age - wouldn't even need an easel for that. Completely different story with modern ILFORD RC multigrade in my experience. I used both regular and top notch easels like Leitz 12x16. Printing mostly 7x9.5 and 8x10.

One way to get "borderless" is to print with enough border to hold the paper flat, and then trim off the border.:rolleyes:

One way to get "borderless" is to print with enough border to hold the paper flat, and then trim off the border.:rolleyes:

 

If I was in the mood to do it, I might try double-stick tape, but that should work, too.

 

Most paper that I remember has enough curl to know which side is which.

 

I believe I had some, not so long ago (a few years) which was so flat that I exposed the wrong side.

 

I suppose with too much curl, and with an easel holding the edge, that it might rise in the center.

 

Modern papers are so fast, though, that I am usually stopped down enough, that there should

be enough depth of field for a small amount of curl. (Well, maybe not for the larger sizes.)

A vacuum easel for paper? Total overkill. However, if you want to waste several hundred dollars and be deafened by the noise - go ahead, but I doubt you'll see any difference between that and the far cheaper option of buying a decent masking frame.

 

My reasonably-priced LPL frame regularly produced pin-sharp prints up to 12"x16". The standard in most of the commercial darkrooms I worked in were RR Beard frames. Their 'Black Prince' model being very popular. It's the Rolls-Royce of masking frames.... at almost Rolls-Royce prices brand new. Although the low demand for darkroom kit today means that they're very affordable used. If you can find one.

tricks on how to keep paper flat

Climatize! Paper, even the non photographic variant, is humidity sensitive. If you place an unpacked pallet of 50x70cm cardboard into a too dry room over the weekend, you'll have serious(!) trouble running it through a printing press on Monday, since it will be most likely no longer flat. - Imagining how much abuse the carrier stock of your Multigrade has seen in Ilford's factory and on it's way into your darkroom: No wonder it is curling.

If you aren't contact printing; why don't you stop your enlarging lens down, to gain the sharpness you are desiring? - I wouldn't blame absence of paper flatness in my easel for a lack of sharpness. - How about bad enlarger alignment instead?

Otherwise I'd guess there is nothing wrong about a vacuum plate. Vacuum frames, where a rubber backing gets sucked against a glass plate, are nice for contact printing (although not every offset plate I tried to contact copy turned out fine).

Quite some wise and reasonable answers here, thanks folks. Interesting point about climatization too.

 

I am quite happy with sharpness, and enlarger Leitz Focomat V35 with Focotar 40mm lens is very stable and is doing terrific job, and of course I am stopping down. The paper is so bent that sometimes it just feels wrong/annoying, and I thought I could just solve it in one shot with vacuum plate. But reading the answers here, it seems like an overkill at this point indeed. Better to concentrate on negative and printing quality with what I have already instead, and consider vacuum plate at a later stage maybe.

As well as I know, fiber-based papers tend to have more curl than RC.

 

But I much more remember the curl of dried fiber based prints from the days before RC.

I suppose paper flateness inside an easel shouldn't matter. - hitting an online DOF calculator your 40mm should deliver 1,7cm of DOF in 30cm distance at f5.6. - Even if we are picky and believe into just one third of that, it is still more than the paper curl that an easel would permitt. In doubt do a tiny test stripe of the not sharp enough area, to proof that paper flatness didn't cause your sharpness problem.

Many moons ago, when I had the luxury of a darkroom, I used to counteract paper curl by placing the reverse of the sheet over the edge of the table upon which the enlarger base was fixed (other end of column bolted to ceiling) and, wearing clean cotton gloves, gently drag the paper across the edge, pulling it slightly downwards, thus imparting sufficient reverse curl to make the paper flat enough to use a Paterson magnetic borderless easel for prints up to 15x12. Practice in the light with test prints until you know how much pressure and force to use.

I've taken to using double sided tape when making prints that are too large for my easels. These types of tape are available with differing adhesive strengths (tackiness?) from one side to the other. You can place them on your work surface without them sticking to the back of the print. Works great and very cheap.

Hmm... I always put bricks

on top of my curled paper...

http://bayouline.com/o2.gif

- hitting an online DOF calculator your 40mm should deliver 1,7cm of DOF in 30cm distance at f5.6.

Except the conjugate focii are reversed in an enlarger, with the negative being the subject and the paper being at the image plane. So what's needed is the depth-of-focus.

 

Plugging the reversed numbers into a DoF calculator, a 40mm lens at f/8, at a magnification of 8x and with a CoC of 0.1mm, gives a depth of 'field' of just over 0.2mm. A bit different!

You don't want to rely on a lot of DOF with an enlarger because when you stop the lens down by more than about two stops, you start to get into diffraction, at least with any decent lens. I remember some old fiber double weight paper that you'd have to stand on to keep flat. Mostly my LPL had no trouble keeping paper flat.

a depth of 'field' of just over 0.2mm.

Good point! - So @oleksandrk should question his negative carrier and film flatness (in case of a glassless one) instead of the easel and paper flatness?

Good point! - So @oleksandrk should question his negative carrier and film flatness (in case of a glassless one) instead of the easel and paper flatness?

Maybe. The real point is that depth-of-field isn't applicable to the paper side of the lens. The 'subject' being projected is the negative, and the sensitive material receiving the image is the paper.

The depth-of-focus works out to around +/- 7mm, but of course the print wouldn't be grain sharp over that margin, just acceptably sharp at a normal viewing distance. However, even if you divide that number by 10, that's still a heck of a lot of paper waviness.

Sometimes paper starts to curl the minute you remove it from its box. When that happens, it can be difficult or impossible to keep the projected image grain-sharp throughout, even with a glass negative carrier. It is noticeable even in 8x10 prints. There may be other factors at play too, including field curvature of the lens, or the negative not parallel with the enlarger bed. Vacuum platens are in common use in the graphic arts business, including framing and matting. Making one for home use is an intriguing idea. As you surmise, very little vacuum is needed to keep the paper flat.

 

My main concern would be distribution of dust by the vacuum pump. An HEPA filter on the discharge would be a good idea.

 

Is it worth the effort? Going soft at the edges is not necessarily a bad thing, depending on the application. Being "grain-sharp" is akin to "pixel-peeping," which is widely deprecated by people who can't achieve it (or don't care). Fuzzy edges are easily visible in landscapes, architecture and murals, distinguishable from merely being out of focus.

I've taken to using double sided tape when making prints that are too large for my easels. These types of tape are available with differing adhesive strengths (tackiness?) from one side to the other. You can place them on your work surface without them sticking to the back of the print. Works great and very cheap.

 

This is interesting idea. I thought about that too, but was a bit concerned with glue particles going into chemistry and making a mess of easel/enlarger board. Though cleaning the paper and the board with a damp cloth will likely solve these issues. Since this would need to be applied only on selected/large prints, it doesn't sound like a lot of extra effort either.

My main concern would be distribution of dust by the vacuum pump. An HEPA filter on the discharge would be a good idea.

 

Is it worth the effort? Going soft at the edges is not necessarily a bad thing, depending on the application. Being "grain-sharp" is akin to "pixel-peeping," which is widely deprecated by people who can't achieve it (or don't care). Fuzzy edges are easily visible in landscapes, architecture and murals, distinguishable from merely being out of focus.

 

I think it becomes worth an effort when negatives are really good enough to print them in the highest quality possible on a large size paper :) Once I get there I would seriously consider this, also given that vacuum boards of solid size are affordable at relatively low cost. There should be no problem to find appropriately quiet vacuum pump, and good point about dust distribution/filter too.

There should be no problem to find appropriately quiet vacuum pump

No matter how quiet the pump, the inrush of air through the uncovered holes creates a loud white noise. Nobody that's used a vacuum bed would go out of their way to work in the same room as one. And no commercial darkroom I ever worked in or visited used a vacuum easel for paper. Film, yes, it's the only way to pin large sheets of film to a process camera back, but for paper printing it's just a waste of resources. Even for mural-sized prints.

 

As shown above; the depth-of-focus on the paper is huge compared to the depth-of-field you have on the negative in the enlarger.

As shown above; the depth-of-focus on the paper is huge compared to the depth-of-field you have on the negative in the enlarger.

 

Thanks [uSER=2403817]@rodeo_joe|1[/uSER] . I verified that once by lifting the focus finder a couple of mm up from the board and seeing that image is still in focus. It was not many mm though before image went out of focus on a 8x10 enlargement. I think you're right, it still provides very good margin even against relatively bad paper curls. Maybe it wasn't even smart to open this thread, but nevertheless it was interesting to read about various points and experiences. This forum is fantastic.

Except the conjugate focii are reversed in an enlarger, with the negative being the subject and the paper being at the image plane. So what's needed is the depth-of-focus.

 

 

 

Plugging the reversed numbers into a DoF calculator, a 40mm lens at f/8, at a magnification of 8x and with a CoC of 0.1mm, gives a depth of 'field' of just over 0.2mm. A bit different!

 

 

 

This is wrong. How can you reverse-plug the numbers and not reverse where the calculation applies to? Since you are plugging the reverse numbers and you are treating the negative as the subject, then that calculated DoF applies to that side of the lens. Also, if you are reverse-plugging the numbers, then if you treat the negative as subject then you can no longer use the 30cm distance in your calculations as the focusing distance, you'd have to use the distance between the lens and the negative.

 

 

 

 

 

 

Having said that, such DoF calculations for prints are not practical, CoC is based on assumed viewing distance of the image. I'd use it as an estimate only.

Edited May 1, 2020 by mateusz_broughton