Fastest UV print source?
I am doing some centennial pop prints and using my standard BLB bulbs for exposing the prints. I have 4 24" bulbs and am doing 5x7 prints right now. The exposure times are over an hour for the proper contrast negs, which are of course very dense. Or is it me that's dense?
Does anyone have any suggestions on how to shorten these exposures? Are BL bulbs going to give me any more speed? What about other light sources? I am looking for anything that will shorten these exposures. I would prefer to use an artificial source to stay fairly consistent with print times.
Unless I'm remembering it backwards, BL bulbs have more UV output in the right wavelengths than BLBs.
And there is always sunlight but tougher to get repeatable results if you want to make "editions".
I am in the same position as you. I have a box I built with 8 24" BLB bulbs in it. With Centennial POP my exposures range from 45 to 180 minutes. I am also trying to figure out whether I need to either re-build my unit or just get a timer that handles long times. There is a Gralab timer out there that will do up to 15 hours. Here is a link to their site:
What I do is just expose the prints while I am doing something else - like sleeping. I am using a Gralab timer that times up to 60 minutes. If the times are longer I just keep track and turn it on again when I think of it. I just accumulate the prints in an old film box and process when I have 6 to 8 prints.
AmerGraph ULF-28 . I use a NuArc 26 1K and love it. With the light integrator you can really dial in exposure times. When it comes time to get a new unit I will go with the Amergraph ULF-28. Faster restrike time and it uses a new CWX lighting technology. Contact Sandy King, I think he was one of the beta testers for these units. At least I know he uses one anyway.
Originally Posted by Harrigan
BL tubes will not shorten print times by very much. I have tested the two types of tubes several times in the same light fixture and the gain in speed with BL is less than 1/4 stop, not worth the trouble and expense of changing the tubes if you already have BLBs. The tests included several processes, but not POP. However, POP is sensitive to the same radiation so I would expect similar results. BL and BLB tubes radiate about the same amount of light in the useful UV range. The difference between the two is that the BLB has a filter than cuts out all light in the visual range. But alternative processes are not very sensitive to visual light, so the net impact on printing is minimal.
Exposures of an hour or more indicate that your negatives are over-exposed. POP, and most other alternative processes, require negatives of high contrast, which you get with long development times, but they do not require dense negatives, which usually indicates over-exposure.
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Sandy's got it right. It's not your light source, it's your exposure. Your negs are way denser than they need to be. It's density RANGE that's important, not overall density. I use a UV box with 12 4-ft BL tubes and my POP times are generally under 10 minutes. Typical neg for me would be FP4 developed in Rollo Pyro.
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My Nuarc 26-1k is one of the best things I have ever invested in. I would never go back to BL bulbs. If you can find a used one in good shape, at a good price, its a no-brainer. I got mine at a university surplus sale. There a quite allot of them around, because they were widely used industrially, have been obsoleted in may cases, and so are sometimes almost given away.
Nuarc 26-1K, puny little thing, no power ... Real photographers use:
Coming back to earth, platemakers often sell for less than the table-top printers. Usually the bigger the unit the less money it sells for. Old platemakers are often 'free if you will haul it away' . The small ones are the size of a small washing machine and usually need 220V. Power is 1kW for the table-tops, 2kW-4kW for small platemakers are 6kW for the large ones. The carbon-arc boxes work well and are just about always free.
'Overhead' units or printing lamps are other alternatives to consider. The nuArc OH1500 is an overhead HID printing unit with a small compact bulb and reflector for high definition imaging and is ideal for most alt-process work.
There are a dozen different makes - nuArc and Amerigraph are still in buisness and can supply service, bulbs and spare parts. Search for "plate maker" "platemaker" "plate burner" "plateburner" "exposure unit" "overhead exposure" "nuArc" "Douthitt" "Amerigraph" "Burgess" "Dianippon" "Olec" "Theimer" "Teaneck" "Sandmar" "Agfa" ...
Silk screen exposure units are the same except for the design of the vacuum blanket and frame.
Keep in mind anything over 1500 watt will require a heavier 20 amp line to run it and it will not run off of a normal household current. I ran a separate 20 amp line dedicated for the 1000 watt 26 1K so as not to have any line draw from any other source. The 1000 watt works beautifully with short exposure times around 350-500 units and can contact print 20x24 with no problem. The vacuum table is a must as far as I'm concerned when you get into ULF negatives. Also the 26 1K has a very small foot print if darkroom space is an issue.
Thanks for the responses. I will try reducing my exposure next time but I didn't really over expose the neg on purpose, I simply gave it more processing time than I would have for a regular silver print. I exposed as I normally would for bw and increased my processing in an attempt to get the right highlight density for pop.
Well obviously you guys think the neg is way too dense so it must be the problem. As long as you're telling me I should be printing centennial pop in the 10 minute range with the BLB's I certainly need to adjust my exposure technique for this process.