20х24" enlarger

[Tin Can]

You may find a source at this 'Toy' store, which sells robot parts, distance sensors and controllers.

I shop there and they are a reliable supplier. Watch the videos!

https://www.pololu.com/category/189/...-range-finders

[mamanton]

Source needs to be oversized and the size would depend on the enlarging lens angle. Edges are horribly uneven. Also, remember no such thing as a perfect diffusor.

BTW, there is a new plastic diffusion material that uses air bubbles instead of white for diffusion. It is suppose to be more diffuse and efficient. Another trick I've seen for holding 8x10 negs flat is to have an aluminum frame to which the neg is held flat with simple clamps at the edge. Once inside the enlarger, the heat expands the aluminum more than the negative and pulls it tight. Not sure that this would work with sufficient flatness for 20x24. Depends on the temperature coefficients of expansion for both materials, but this can be calculated.

Lots of advantages to horizontal since gravity works in your favor. I can see while reviewing this that the neg carrier could be heavy. It would be good to calculate its weight early and consider how the neg is installed and moved into position. Might be easier to clamp opposing edges that hold the neg in tension with springs or weights. The business with the laser alignment seems a bit of overkill, but I have never designed with such things.

Hope this helps. Disregard after reading. --ew--

Many many thanks! Your ideas are very clever, I'll keep them in my mind.

[mamanton]

IMHO, having a huge enlarger for something like a 20" X 24" neg sounds cool, but if the print will only be 20 X 24 (1:1) it's a lot of work/big commitment to build the beast in the first place... (WH Jackson did OK with those large contact prints...) Maybe work on bigger cameras for bigger negs that can be contact printed would be OK...

Another possibility for light stage coverage is the use of a large fresnel (+ diffuser?) near the negative, with the lamp farther away at the focal point... These can be had from old large screen projection TV's, and can be surprisingly even if set-up very carefully... (I sometimes use one for a "daylight" light source studio effect using a small lamp at a distance...)

Good luck,

Steve K

Thanks, Steve! Firstly, we thought about an enlarger slightly bigger than 8x10, let me say for the negatives 11x14, 12x20.... But we recognized that it would be still a lot of work, and we decided to create an enlarger with a reserve for the future - 20x24'' - maximum format we can imagine ))
Once we decided, next month we were very lucky bought the 20x24'' camera )) No way back!
And we are very like Heiland LEDs splitgrade system. Most comfortable printing system. We'll use it in 20x24''!

[Drew Wiley]

Well, I'll never build my dream enlarger. I came as close as I could on my budget and machinery limitations. This was slightly pre affordable steppers and full sine wave control, which I would be wary of even now due to dependency on specific software and its inherent short lifespan. So I gotta put up with triacs going out every now and then, and the headache of having to employ a block and tackle to remove and replace the colorhead even for a basic lightbulb change. It's a huge vertical machine (to save floor space), true narrow-band additive color, and the colorhead runs relatively cool due to its special yet oversized design. The vac easel itself is built like a tank. But I see absolutely no means of escape from precision glass carriers. Get a copy of one of those old Kodak Graphic Arts Guides, or similar tech literature from Stoesser etc. They give actually coefficients of expansion and contraction on polyester (mylar, Kodak Estar film base, etc). And polyester is the standard for film stability. Acetate is awful. Glass also isolates the emulsion from dust landing on the in-focus emulsion itself due to ventilation inside the system. The benefits greatly outweigh the headache of having to clean repeatedly clean glass. It's better than endless spotting afterwards.

[mamanton]

Concerning the movement of cooling-air affecting the neg, is it not possible to use the diffuser as a 'wall' between the LED- array and the neg? Or is there some technical requirement to have the LEDs and the neg in the same airspace?
I suppose a neg carrier would most simply be based on tension, by means of edge-clamps and parallelograms in the same plane as the neg. The corner springs used in some carriers for 4x5" and 8x10" would be impractical for anything larger (if they ever worked anyway). The question becomes whether sufficient tension can be applied to remove sagging (the tension frame would help with rigidity of course) without destroying the neg, or stretching it.
Edit: Might a light-source using studio-flash into a diffuser-box remove cooling, cost and complexity problems tied up with the LED head? Two exposures, or two flash units, would provide the light for variable-contrast papers but dodging and burning might be tricky!

For sure, it's possible to use any kind of diffuser between LEDs and a negative, even a normal milky glass, or some kind of mixing box.
No way to turn us out from the LED cold light source ))
Thank you for the interest and advices!

[mamanton]

Overhead rail system with stepper motors on the back and forth for the unit as well back and forth remote control of the fine focus, This most likely would require a Durst Style Negative stage, but biggie size.
The lens would be of the finest quality and speed.
The lightbox / power light unit has already been designed (Lisle Camera) so I know this works.
Creating Magnification Charts is easy if you are so inclined for changing paper.
The wall would be adjustable with a very good vacumn system and within the room everything would be painted black, of course a econoroll for paper delivery and cut.
We have tried to have paper dispensers on the vacumn walls in the darkroom, I never saw one that worked to my needs, placing magnets for positioning and kicking on the vacuum when paper is in place is very easy.. On a very good day at Jones and Morris Photo Enlarging I could put 5 boxes of paper on the wall - that is a lot of paper.
2 times magnification is 40 x48 - three times takes us out of the realm of commercial made paper.
For me the problem would be the Camera Stage , being able to get a good technical negative not to mention something I would like to print.

We already have the totally black walls in the darkroom, and the enlarger on the rails - DeVere 508H with motors for distance and for fine focus. It works. We calibrated it, and it works. Why not to try something new?
Vacuum walls is a question... Firstly we didn't find the wall in a big size. Next, you need to cover all the halls around the paper, if you print not a big photo, like 50x70cm (20x27''), next big problem - dust, next noise - or you should bring the vacuum machine to another room... oh... to complicated.
Another option - electrostatic wall! Very expensive, and did't see how it work, only heard about it.
We found that magnets are working very good! We already printed 110x220cm photo from 6x12 negative, and 110x140cm from 8x10''.
Now we are waiting for the renovation and some modification of Donchev 20x24'' Camera plus tripod - but it's not a theme for this thread.

[mamanton]

You may find a source at this 'Toy' store, which sells robot parts, distance sensors and controllers.
I shop there and they are a reliable supplier. Watch the videos!
https://www.pololu.com/category/189/...-range-finders

Thanks a lot!!!

[LabRat]

Have you considered finding an old graphic arts process camera and converting to a ULF enlarger??? (There are many sitting around unused, and can cost little or nothing, or the owners might even PAY you to take it away!?!!! Might even have the lens set, and other goodies...) That way you can concentrate on a light source + neg carrier... It might have the copy easel that can be used to hold paper, or the rear vacuum easel can be converted if large enough... Would get you up and running faster than a ground-up build...

Steve K

[Eric Woodbury]

A friend of mine that prints 8x10 constantly needed a replacement V54 tube. He was using the T12 V54 (which he wore out, that's how much he prints), high intensity, which is about 50% brighter than standard. So he built a simple LED light source with white (4200 K) LED tape strips. He used 20 each, 12 inch strips at 4.2 Watts and 340 lumens each. Final product is 2/3 stop slower than his high intensity V54 tube was. There's a fair amount of info here, but it needs careful consideration. He used white LEDs, so he is probably wasting about 30% or more of the spectrum and energy, as the paper will not see the yellow, orange, or red. Using GREEN and BLUE LEDs of equal efficiency will give more usable photons per watt than white, filtered LEDs. This is 84 Watts into 929 square cm. He has used the same old box to mount his LEDs as the T12 cold light. No fans, no cooling, no problem.

If we scale this to 24 x 28" (oversized), that would be 4335 sq cm. (4335 cm^2 * 84 Watts / 929 cm^2 = 364 Watts. If you get all of that into the proper spectrum, you'd probably overcome any loss of light compared to V54 coldlight, which is very bright in my opinion.

Furthermore, if one were to mount, say, 1000W of LEDs to a 24 x 28 x 0.25" (61 x 71 x 0.6 cm) aluminum plate (7.5 kilograms), it would heat at about 9C per minute. In the above example, it would heat the plate at about 3C per minute. This is not much heat. There will be some convection and I've assumed none. No fans required. For best stability, as mentioned above, current source drive is required. YMMV.

[Eric Woodbury]

I should have mentioned that a LUMEN is relative to the human eye response (we see green very well and the ends of the spectrum hardly at all, i.e. not blue or red), while paper 'sees' green and blue about equally well, but not much past the green (yellow, orange, red). Given all those variable, it's almost impossible to accurately calculate what the paper response will be to any particular LED, especially white LEDs which are blue at heart and augmented by phosphors to produce lines that trick your eye into thinking it is continuous.

Have a lucky day. --ew--