I'm revisiting some projects I asked questions about earlier...
Joe, I'd be curious to see your preflashing machine. Tonight, per your recommendation, I bought an S11 bulb and a socket. I had soup for lunch. How do you house this device? Drill a 3mm hole in the bottom of the soup can? If so, how do you enclose the top and make it light tight? I'm sure I could improvise something, but if you have a good way, I'd rather hear it first.
Also, the bulb I bought is clear, not frosted. Does that matter much? Should the light be more diffused?
I use a frosted white bulb, so I can't say for sure regarding the clear one, but I'm certain you can get it to work.
Originally Posted by bvy
I have an aperture stop on the bottom of the soup can. I don't have a photo of the setup available, but I'll do my best to describe it.
The soup can is upside down; the power cord goes through a hole in the top; I use a rubber grommet to keep the metal from chaffing the insulation on the wires.
The wires are short enough to permit the socket and bulb to hang inside the can without protruding out the open bottom.
I have an aperture stop covering the bottom, with about a 3mm hole. The hole size isn't important, except you will want to calibrate the size to permit adequately long preflashing times for your process, based on how far above the work surface it is suspended. I hang mine about 30" above the table; this height was chosen only because it's conveniently located to hang off one of the parts of my Beseller 4x5 enlarger. The important thing here is that it's far enough above the table that the light distribution is even; too close to the paper and the center may get more exposure than the corners.
I'm not certain about ventilation in the can to keep it from overheating; my design uses a plastic flange from a 2" plumbing fixture, that fits inside the can's opening but permits a bit of air to get around the edges. A black paper disc is inside the opening of this flange, with the aperture stop. The insides of the can and the plastic flange are painted black. You could just try a piece of black craft (scrapbooking) paper, taped over the opening in the can with black gaffers or electrical tape for starters, then see if the can heats up too much.
As for the non-frosted bulb, if you're worried about the small aperture in the light source producing some pinhole imaging artifacts of the bulb's filament, you could perhaps use a small piece of wax paper over the aperture in the can, which should diffuse the light enough.
Again, it's a simple device; the whole intent is to permit preflash times that are repeatable, by them being sufficiently long (like 5-10 seconds) in duration so as to permit use of a darkroom enlarger timer.
Good luck, hope to see some results soon.
Okay, Joe, thanks for checking in. I guess the point is that this isn't rocket science. The idea is to expose the paper uniformly and in a controlled and repeatable manner.
I might pick up a new bulb -- or just try the wax paper as you suggested.
Someone else here suggested a yellow filter and showed some pretty impressive with/without results. Do you have any experience with or thoughts on using a yellow filter for exposing paper negatives?
No, I haven't tried the yellow filter trick, which, as I understand it, permits the use of multigrade paper to gain a more moderate contrast image, the yellow filter removing lots of the blue/UV light that activates the high-contrast portion of the multigrade emulsion. Since I use graded paper, it's much less contrast sensitive to the color of light and hence doesn't need the use of a yellow filter.
I've found a combination of preflashing, along with controlling contrast by the use of graded paper, seems to deliver a good paper negative tonal range; I'm assuming that using a yellow filter will give one a benefit for MG paper similar to using graded paper (and which others have reported good results); although you might have to increase your exposure times to compensate for the loss of light from the filter, so perhaps graded paper might permit shorter exposure times (but I'm not certain on this last point, a lot depending on what exposure index you rate your paper, and your developer strength, etc.).
None of this is rocket science, it's more about keeping good notes and figuring out how best to work with the materials. And I'm looking forward to seeing your images.