Making a UV projector for alt-process prints

koraks · 2025-08-16T03:10:43-0400

Wow, that's really neat! Some kind of vacuum frame that sucks the paper onto a perforated plate would be ideal, yes. Not sure if it's very feasible though.

AndrewBurns · 2025-08-16T03:26:13-0400

Here are some bad phone photos of an A3-sized print I just made, will give them a go with coffee toning tomorrow.

Here's the print, using an adjustment curve made with the test print I made earlier today, maybe a little bit on the light side but we'll see how it looks after toning.

For an idea of how sharp the detail is, here's a zoomed up shot of the radio tower (best I could get with my phone camera, but the detail is extremely fine).

The corners are a little blurry because I literally stuck the paper to my garage door with magnets and rolled the projector into place on a trolley!

Another thing I want to try sometime now that I have a working UV projector is exposing some kind of pigmented emulsion coated onto glass from the rear side of the glass.

Ethan Brossard · 2025-08-16T12:46:30-0400

AndrewBurns said:
Digital projector has made its first real print! There are a lot of quality of life improvements to make to it, but for now it's usable.

This is just after washing so it will darken a fair bit as it dries down. Ignore the very rapid tonal transition from blue to white, cyanotype always seems to do this with these LCD screens, I presume it's some combination of the technique having an abrupt tonal transition and the LCD screens having a pretty high contrast ratio.

This was a 30 minute exposure at ~350W LED power which is about as high as I want to go. Projected image is about A4 sized (smallest I can project). Focused by eye (through UV laser glasses!) and the image is very sharp and contrasty. There's clearly a slight vignette, which is inverted, so the middle of the frame is darker than the edges, but I should be able to compensate for that easily enough.

What I really need to figure out now is how to hold the paper perfectly square to the projector and keep it flat during exposure. I used a combination of tape and clips to hold this small sheet to a plastic board but during the exposure the paper still bowed slightly, probably from temperature change. Some sort of vacuum frame might be the way to go, but I'm not sure where I could put it as I'm kinda space-constrained.

Very nice! the large amount of white areas make sense. The cyanotype process requires a relatively low contrast negative, and these LCDs are very fairly high contrast compared to a film negative.

AndrewBurns · 2025-08-17T03:43:23-0400

I had a crack at making the largest print I could fit into my washing tray (58x42cm) and it worked but it was a bit of a dud as I think I under-exposed it by about a stop. I gave it 1 hour 15 minutes but probably more like 2 hours was needed, I had to run the LED at a little less power because at these bigger enlargements the LCD gets a tighter focus of light and I was worried about heating.

Another thing that I'm seeing are concentric rings in the prints from the fresnel condensing lenses, only in the corners of the prints, not really noticeable in the smaller enlargements but getting quite obvious in the big print. I'm not entirely sure why they're showing up as the fresnels should be significantly back from the focal plane of the enlarger lens and so should be quite out of focus, but they're definitely there. I might need to look at some kind of diffusion on the light either between the two fresnels or after the second one to try to get rid of the rings.

Realistically I think the A3 prints are as large as I should be going with classic cyanotype, exposures over an hour are getting a bit silly so if I want to make big prints I either need to look at faster cyanotype formulations or sort out SbQ.

Making a UV projector for alt-process prints

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