Images, plans, sources for cheap bulbs, etc would be welcome.
One of these days I really have to draw up some plans. It will be difficult, because my frames use overdrive ballasts, and that is not a UL, CSA, etc. approved way of doing things. Whenever I discuss the wiring of such tings, I always add lots of disclaimers.
A good source of cheap bulbs is, believe it or not, Home Depot. I bet Lowes would do just as well. They're also a good source of a ballast suitable for overdriving.
The ballasts, unfortunately, are about $25 each, and each ballast only drives two bulbs. They're instant start (no glowing filaments!) electronic ballasts built to drive four T8 34W tubes, when you connect them to two T12 40W BLB tubes, they drive the BLB tubes to a ballast factor of about 1.2 (I measured the exact drive once, but have since forgotten what it was). Regular hardware store 2 bulb magnetic ballasts only have a ballast factor of about 0.6 (because of some really stupid energy saving regulations). So I get just about twice as much light from each tube as the stock magnetic ballasts that you see in all the internet plans.
Now, speaking of the internet plans, not one of them puts a metal plane under the bulbs. The metal plate performs two necessary functions: a ground for starting the tubes, and a reflector. If you like your bulbs to come up quickly and reliably, the starting plate is the ticket. Ground it to your third (green) wire on both the cord and the ballast cases. As a reflector, it reflects light headed in the wrong direction that would have otherwise been largely absorbed by a hunk of plywood. The BLB bulbs are virtually transparent to UV, so they'll not interfere with the "recovered" light. Overdrive = more output, better starting = more output, reflector = more output.
Yeah! Power! Yeah!
My basic plan is to use 3 or 4 ft. BL lamps in a vented plywood box with the bulbs facing up. Plate glass will go over this, and then my neg/paper/foam on top of that and weighted for close contact.
Well, unless you're using some very thick plate glass (in which case, you need to use "low iron" or "decolorized" glass like Starphire) the pressure will bow the glass. This causes two problems. First, it reduces contact pressure in the center of the image, causing the center and the edges to have a different image character. Second, since your concept puts the glass over the tubes, bowing will bring the center closer to the tubes than the edges, so the center will be slightly more exposed. This doesn't hurt most images, however.
Also, working face down may make it harder to achieve a good alignment between negative and paper, especially if you've planned emulsion brush strokes to interact with the print.
I would have the lights perch over the exposure frame, and slide out on double extension rails. My own light source has a 1/2 inch plywood base, thin foam over it, and a thick (3/8 or 1/2 inch) piece of Starphire.
I think I'll incorporate a cover for the whole thing so it can be used as a worksurface when not being used for exposing.
A downward facing source makes that so much easier.
My frame is a design I call an "electric window", because it also serves as a gorgeous portrait light. (seriously, two 2 foot by 4 foot frames, each carrying a dozen Chroma 50 bulbs, running overdrive at about 60W each, is 1440W of high CRI fluorescent light, with an output equivalent to about 6KW of tungsten, but a much better color temperature. And the 2 footers lock together to form a 4 foot square).
I build them the same way for shooting lights and UV exposure. 1x6 inch "white wood" (clean pine), white ash, maple, or red oak, depending on my mood. White wood is the cheapest and lightest.The 1x6 gives you a 5-1/2 inch frame. The wood is 3/4 inch thick. Everything is contained within the 5-1/2 inch thickness. A 3/8 inch plywood panel divides the frame into two sides. The ballast side is 1-1/2 inches deep (as are the ballasts) and the bulb side is 3-5/8 inches deep. The reflector is thin aluminum (I've even used aluminum foil) over the board on the bulb side. You need 1000V rated 18 gauge wire to wire the sockets to the ballasts, that's a pain. I wire them so that alternate bulbs are on different ballasts, and each ballast can be turned on or off individually. That way, I can shoot them with 1 of 4, 2 of 4, or 3 of 4 bulbs turned off, and when they're in 1/2 or 1/4 power, the bulb spacing is still good.
My current three 2x4 foot frames, 5-1/2 inch thick, can be locked together into a 16-1/2 inch thick, 2 foot x 4 foot assembly that can then be tossed into the back of my explorer and carted to a location.
) , and very well thought out.