Projects to aid 50" panoramic prints and darkroom nic nacs

[resurgance]

Great to get up to date on all sorts of new thread on all sorts of topics....
Have been absent for a year or so with life being life, and am rekindling the darkroom 'fire'....

Was investigating making a vacuum easel to suck flat what I would call large prints (600 x 1200mm, or 2ft x 4ft) and am now confident that I have come up with an OK plan, involving alloy plate with 1mm holes at 10mm centers, and an alloy ribbed system internally to hold 'platter' dead flat but keep weight down so my Devere base does not sag. Looking like I may be able to get it around 10kg which is probably not far off the current base which I will remove. It is not magnetic, so nice magnetic strips are out, but I think as I will always have a factory edge as my paper roll dimensions match the sides i should be able to use clamps and an RHS extrusion to get same end result and keep it square.

Another project is to be a roller that goes in custom made SMALL trays to automatically scroll the print. Have now a pretty decent mental image of what this thing is going to look like, and have located all of the materials. Will be constructed from Acetal, with acetal gears on one end, a paper holding method, and a DC gear motor with a built in encoder so I teach it different lengths and have a simple high speed counter to reverse the paper before it strains. The trays can then hold easily less than 3L of chems and have a small footprint - maybe even match the contours of the rollers.

The roll of paper is an Ilford 50"x90ft roll of that 'new' FB Glossy emulsion, I have not printed on it yet, apparently the grains are smaller etc etc. I plan to make the rollers 50mm diameter and have the 1200mm long print go its length through the chems in about 8 seconds per pass.

Just wondering if anyone had attempted this, or used a similar setup, as I have seen photos of an italian or french contraption that looked like it did just this.

Would like to hear please about any potential pitfalls, and things like - would i be best to pre-wet the paper prior to putting through the developer to let it 'settle' and things like that that I may not have considered? Open to any suggestions or experiences.

[ic-racer]

I was going to make some troughs like shown in this video. I'm still thinking about it, but currently only doing 16x20" in regular trays.

[bob carnie]

I was going to make some troughs like shown in this video. I'm still thinking about it, but currently only doing 16x20" in regular trays.

This is exactly how I do large lambda fibres and prints bigger than my 30 x40 trays... doing some 6 footers this month this way for a new show coming to Toronto.

[jon.oman]

In the 70's, I made prints like this that were 50" x 120", while working for Ford Motor Co. We had SS sinks that were trough like in a line. We rolled the paper stock just like the video.

[resurgance]

Thats the way I'll do it to start with for sure, I understand now what is meant by 'scrolling'. I would be keen with the larger prints especially with wash-aid, and prep for selenium as well as selenium to automate the scrolling of the print? Essentially I will be doing as per the youtube clip but with a mechanical aid. Well I'll see if it works without pre-wetting the paper, I guess the only real way to figure it all out is to do it.
Previously I have only processed using trays, and only done 16x20 max as you say IC-Racer.

6ft. Bob that is a decent print! I have only just started getting an idea of just how much detail is contained in a decent neg, and I have not even gone past the print size where it becomes obvious/noticeable. I am really looking forward to enlarging a 4x10" neg onto a 2ftx4ft print! Provided obviously that I do my job with the loupe properly on the ground glass when making the neg to start with.... Am really fond of using the view camera to produce angled focal planes; its uncanny how it affects the print, and such a nice thing to look at - also watching a photographer who has always had his focal planes parallel try and figure it out is a treat haha!

Great to get excited again about this great art, and the wet process.

[resurgance]

Is there a calculation for actual depth of field with enlargers? For example, tonight I cut a 600mm bit from my 1250mm wide roll (or 24" x 50") and taped it onto my baseboard. It was almost flat, but using my eyecrometer I detected very scientifically using my index finger that in certain parts that fought the natural curl, the paper was around about 2mm off the baseboard.
I am using an 8x10 enlarger and 300mm lens, I always stop down 2 stops. Also the baseboard is accurately aligned with the film plane via a precision level etc.
With any luck I can postpone making a vacuum easel for a while, and just get to some printing, until I free up some spare time.

[resurgance]

Hey! IC-Racer I just saw a post you wrote in 2010 about enlarging lenses;
quote
"Isn't stopping down an enlarger lens also helping to overcome the curving of some types of FB paper?

Perhaps in some settings. Here are some numbers (based on CoC 0.15mm):
The focal depth on the baseobard side at f5.6 with a 5x enlargement is 2.5mm. When stopping down for a print (f22) the focal depth at the baseboard is 43mm."

Thats gold - so tell me, do you happen to know where you got this info from? or is it done with your eyeball? I just tried to tape a piece of FB 2ft x 4ft paper from a roll onto my baseboard and I could see it was mostly flat with a chance of rain; I am using a 300mm lens, 8x10 enlarger, roughly 2 - 3ft enlarger height, stopped down two stops.
What this means to me is that I will be able to produce some decent prints WITHOUT a vacuum easel! Keen to hear your thoughts.

[Nodda Duma]

Hi resurgance,

I'm jumping in as a lens designer to reinforce your conclusion that you will probably not need a vacuum easel.

Math discussions are typically pretty boring, but I think the depth of field calculation is really useful for your current endeavor. The tolerance in "sheet curl" or focus accuracy required is the depth of focus. This can be calculated from basic parameters of the optical setup.

Probably the most useful form of the depth of focus equation is based on the enlargement of the print (magnification):

t = 2*f/#*c*(1+m)

where

t is depth of focus
f/# is the enlarging lens f/# setting
c is the acceptable blur spot size (Circle of confusion in optics jargon)
m is the enlargement magnification.

Circle of confusion is usually the point of contention, and I'll just say that it's a deep discussion beyond the scope of this thread. A common circle of confusion "rule of thumb" for a negative is d/1500, where d is the diagonal size of the negative. That value would be magnified by the enlarger magnification for a print-sized circle of confusion (for 35mm, it gets close to commonly used value of 0.2mm for viewing an 8x10 print at comfortable reading distance) IC-racer's value of 0.15mm is just fine for enlarging a 35mm negative.

So as an example calculation, if I were to enlarge a 35mm negative to an 8x10:

magnification m = (8*25.4)/24 = ~8.5x
acceptable blur size c = 0.15mm (I use IC-racer's value mentioned above)
enlarging lens f/# = 8.0

t = 2 * 8 * 0.15 * 8.5 = 20.4mm, or 0.803".

There are a couple of caveats to keep in mind:

1) Be aware of what height the grain focuser is showing you the image relative to where the paper will lay (usually a paper's thickness above the surface that the grain focuser's base is sitting on).
2) The equation assumes your enlarger is perfectly aligned.

For these reasons, I would add a "safety factor" of, say, 4x. So I would want the print in the example above to lay flat to within 20.4 / 4 = 5.1mm, or 0.200"...easily accomplished on an easel.



For your goal of enlarging a 4 x 10" negative to a 2ft x 4ft, or 24" x 48" print, the circle of confusion for the final print will probably be more like 0.91mm (negative diagonal divided by 1500, then multiplied by the magnification determined below). This is just an example .. so define the acceptable blur size based on your assumption / experience / intuition about the viewing distance of the final print.

magnification = 24" / 4" = 6x
acceptable blur size, c = 0.91 mm
enlarging lens f/# = 11.0

t = 2 * 11 * 0.91 * 6 = 120 mm

With a 4x "safety factor", the paper would still only need to lay flat to within 30mm, or 1.18". So I agree, you probably do not need a vacuum easel.


Hope this helps,
Jason

[bob carnie]

Regarding paper on walls for murals.. I have done both magnets to metal wall no Vacuum , and as well have worked with huge Vacuum Walls for murals... I prefer no Vacuum wall just a laser aligned metal wall and a very good set of handled magnets . You will be fine.

[resurgance]

Thanks guys, this is a revelation for me! I think as i have heard over and over that enlarger alignment is critical and to get the sweet grain everything must be dead flat, I just resigned myself to the fact that I was going to build a vacuum easel. And its not that easy to do it properly. I tend to over-engineer things, so it had to be light-weight (to not bend my enlarger subframe as I moved it up and down for bigger prints) dead flat, and not big holes, the right vacuum pump, blah blah. I worked out on my milling machine I was staring down the barrel of between 3000 - 7000 holes.... Humbug.
But now I'm off the hook and I can get on with taking photos and printing. *happy*