UV enlarger? Is this relevant? An enlarger that can do cyanotypes might be able to do POP.
https://www.youtube.com/watch?v=zI1nWHuX3N0
UV enlarger? Is this relevant? An enlarger that can do cyanotypes might be able to do POP.
https://www.youtube.com/watch?v=zI1nWHuX3N0
Photography:first utterance. Sir John Herschel, 14 March 1839 at the Royal Society. "...Photography or the application of the Chemical rays of light to the purpose of pictorial representation,..".
Interesting video...and scrolling down to the very last comment/question, regarding the possibility of using this enlarger for PT/PD - and that this goes unaddressed. Also...nothing mentioning actual glass (lens, condensers, etc.) types, relative to UV transmission, nor anything about other means aside from condensers of focussing/enhancing UV LED light paths - such as parabolic mirrors. My guess is that Mr. Krooshof has already vetted these possibilities...but maybe I'll try contacting him just the same.
At any rate...I just want to thank everyone here so much for not only the great information put forward, but also for being so patient as I've persisted in hammering away at this question.
Yeah, fun video, though I didn't watch all of it yet. And I have no interest in printing cyanotypes, though I do have some lovely antique ones in my collection.
That video is one of the best out there but very lengthy. He doesn't mention the frequency or size of the custom made LEDs he ordered from china, but they must be near uv (395nm) and pretty small, although the quartz lens will make them optically larger. The plastic fresnel lenses would require near uv. He uses the classic cyanotype with a pre-flash exposure, which would require an extremely thin low density range negative with high transmission. Not exactly the type you want for platinum/palladium. Video is mostly about his journey in developing and building the equipment for projection printing cyanotypes without having a workshop. It was his learning process.Originally Posted by John Layton
The majority of historical printing processes are quite sensitive to blue light as well as uv. If using pyro or other staining developers, this can affect the contrast. Sunlight has very little uv light getting to ground, much more blue is available. If you calibrate your process for a particular UV light, this can a problem when the frequency changes.
Parabolic reflectors would have to be off-axis segments to avoid a large hole in the center, so not very useful for condensers. Condensers don't need to be very sharp, either, so pyrex plano-convex pairs were used in enlargers like the Omega D2 with about F:2. Fresnels are much cheaper, and used in overhead projectors widely, some as fast as F:1. An Omega D2 can be converted easily using standard COB near uv LEDs for 4x5, but likely not practical for this use.
Personally, I enlarge my negatives using photographic means without resorting to digital negatives due to the challenge and the pleasure of working with photo chemestry. Anybody can click a mouse but that's not photography. I use mostly ortho-litho films for this and get good results. I will likely experiment with xray films this winter for this as well.
Alan Townsend
Fresnel lenses typically involve a kind of plastic which absorbs a fair amount of UV. So you need a surplus of it to begin with. With contone imagery, Ortho Litho film also tends to have a fair amount of resudual fbf and yellowness which blocks some of the UV; so again, sheer UV muscle is called for. Direct sunlight has lots of UV, and has worked since the inception of these processes; but it varies and takes longer. The first enlargers were based on capturing and directing window sunlight.
All this stuff is fun. I've made all kinds of specialized equipment myself. But if it were me, I go the enlarged duplicated negative route, and contact print it. I don't particularly like Ortho Litho for that application, but have certainly done it successfully.
Kodak manufactured a really great emulsion for doing enlarged negatives back in the day...4125 I think? I understand that Bergger now makes something similar - has anyone here tried it?
To be totally honest...I've never really gotten deeply into PT/PD printing - but would like to try it again sometime. I do have fond memories of sitting out in the sunlight with a contact frame on my lap. A far cry from what I suggest here perhaps...but who knows, maybe I'll soon be out there again - letting nature work its magic!
As a stepping stone, I wonder if it would be helpful to evaluate light sources by making contact prints through a polished quartz plate. They seem to be inexpensive.
I think Bergger Print Film is no more.
It's more likely to be synthetic quartz flats. Blemish-free natural quartz crystal of significant size is incredibly expensive. There was once a secret mine for that on a peak near where I lived,
which got in and out by mules. Even back in the 50's an optically clear crystal a foot long could fetch five thousand dollars or so. The exact location was a closely guarded secret and difficult to get to, and within a designated roadless zone (now an official Wilderness Area). When someone tried getting in there riding a Tote Goat, the Forest Service intercepted them 12 miles in, pulled the spark plug, and forced them to push the thing all the way back out.
Drew,
Near UV behaves more like visual light with optics. Projector optics suppress near UV while enlarger optics have little effect. The 395nm uv leds have a fairly narrow band, but extend from violet through 360nm or so. Both cyanotypes and carbon print tissues respond about half as well to royal blue leds as to 395nm leds. I've measured this recently in testing I've done. I should have included this in my "internet photography lies"l thread. If I built one of these COB led enlargers, I would likely use a royal blue led array, since this is much easier to focus and almost as fast.
Ortho-litho film is quite flexible and about the right speed for darkroom work. For lowest contrast, I process using D23 at 1:7 dilution for 2 minutes with no water pre-wash. This gives a density range of about 1.4` outside on a sunny day. The film does have a nice curve to it, very similar to the curves for cyanotype/vandyke brown, so they can compliment each other. For the positive, I either enlarge 35mm to 4x5 or contact print 4x5 using the same enlarger, and post exposure flashing to fairly high densities to control the contrast. I also dodge and burn in at this step. The very curvey nature of ortho-litho makes it variable contrast via healthy flashing. This does increase the exposure time of enlarging the positives to the final negatives. By changing developing times to make the interpositives and negatives have identical curves with minimum flashing, a very linear curve results, allowing enlarging linear negatives to pretty darned linear negatives for carbon printing. Quite flexible when you figure it all out.
Alan Townsend
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