The Darkroom Automation web site has an application note explaining how variable contrast paper works (and sometimes doesn't):
Contrary to common belief the various emulsions in VC paper all have the same intrinsic contrast. The only difference is that one emulsion has a green sensitizer added to it - it is the same sensitizer used for Orthochromatic (blue-green sensitive) film. This is very old technology, the addition of erythrosine dye to the emulsion to make it orthochromatic was discovered in the late 1800's. Dupont came up with the idea of 2-emulsion VC paper - called Varigam - in the late 30's.
The reason that a high contrast filter is magenta rather than green is that VC filters also pass red light. The addition of red results in more illumination when you are dodging and burning. Try putting a deep blue filter in the holder and then hold a cardboard dodging card under the lens -- it is very difficult to see just where in the image you are with the card. The original VC filters were green to blue in color, but user's didn't like them, and that's where the change to yellow to magenta filters originated. Color heads also use yellow & magenta, while VC cold light heads are stuck with green and blue.
Martin, Thanks for your reply. The exercise sounds like a good idea to me. I did some printing last night and compared a non-filtered print to my #2, #2.5, #3, just to see what would happen. I got very confused as my non-filtered print is drastically different than what I get with a #2 MC filter. Your exercise sounds like just what I need. I'll do this before attempting to print anything else. Now I just need to figure out which of my negatives are "normal" enough to use. :D I think I'll mount the prints on a piece of cardboard to hang in the darkroom for future reference. Thanks a lot.
Originally Posted by MartinP
Just as a matter of interest what could the unfiltered print be compared to grade-wise and what was the paper? If I recall correctly Ilford says that its VC paper unfiltered corresponds to grade 2
I went into the darkroom just now and turned on my enlarger and guess what I noticed? The stupid negative is on Ilford's XP2 (C41)film. The resulting negative isn't black and white, but BROWN and white.:whistling: I feel very silly and you (and anyone else) are welcome to come over and kick me in the ass, as it should have been obvious to me that brown negatives are going to require a different approach. I didn't realize it last night as I'd been under the red lights a long time and I guess I went a little color blind.
Originally Posted by pentaxuser
But for reference, the unfiltered print is lower in contrast and very dark. I am using Arista's RC and FB papers, as they seem to need almost identical exposures as each other. I'll look through the forums for how to best print C41 "B+W" negatives but I will also make the test print grid as Martin suggested. I think it will do me a lot of good.
Thanks for the response. If the print is overall very dark then I wouldn't expect the use of filters to correct that. They will increase contrast and that way appear to brighten the highlights compared to the midtones and shadows so yes parts of the print will look brighter but you need to look at overall exposure as well. If a low contrast but "too dark" print has its contrast raised but at an exposure that simply equates to the "too dark "exposure on the low contrast print then it will still be too dark.
Originally Posted by jeddy-3
I might be stating what is obvious to you but a sparkling print is a combination of the right exposure for the highlights with a right exposure for the shadows so the details can be seen. I agree the exercise of printing at all the grades is very educational
You're correct, it was very overexposed but I had done so purposefully as I had hoped for a very dark image with only a few bright highlights. With use of even the #2 filter the highlights were "overcorrected". I will come back to the print later; I'm trying to run before I can walk.....crazy to say as actually I'm hobbling around on crutches for 2 months.