I recently got a Chromega 4x5 enlarger and am trying to figure out how to change contrast with it for variable contrast papers. The manual only lists M and Y channel values for grades 1 to 3. Is it not possible to go above or below that with the color filters? I assume the C channel just needs to be set to zero. Is this correct. Also, how does exposure need to change between different contrast grades - my Ilford filter set needs double exposure above grade #3 - is it the same here?
Any info on using color filters for BW contrast control would be useful. Finally, am I better off using plain filters with the head set for unfiltered light?
Thanks,
Anupam
Why don't you try split-grade printing to see how you like it?
In short, (you can find longer explanations in this forum) you do a test strip in 3 second increments of a well-exposed negative using only the M filtration, set to its maximum. Pick the strip that has the desirable amount of detail in the darkest shadows. This is subjective, of course. Someone else might like slightly less dense or more dense shadows. Let's say, for example, that the darkest shadow area in which you want to see texture/detail is 10 seconds at f/11 at full magenta.
Then repeat the test strip procedure with the same negative on a new sheet of paper, this time, using maximum yellow filtration. Look for the brightest highlight that just barely contains texture/detail. (Remember in both cases, there will be a dry-down effect of 4-8% depending on the paper, and allow for this.) Let's say, for example, that on the test strip 6 seconds at full yellow gives you a bright highlight that has the desired amount of texture/detail.
Now, run a sheet of paper, giving it two exposures, one at 10 seconds full magenta and another at 6 seconds full yellow.
This should give you a work print that is very close to perfect on the first try. You may need to adjust one or both of your exposures to fine tune it, and you may identify areas of the print where you need to burn or dodge using both or one of the two colors.
A rule of thumb, easily broken however, is that if you want to increase or decrease overall density without changing the contrast, burn or dodge proportionately with both M and Y filtration. If you want to change contrast, burn proportionately with one or the other, i.e., for a harder tone, use only magenta when you burn a particular area; for a softer tone, use only yellow when you burn.
It may be a little tricky at first getting your mind around the concept, but when you do, you will be amazed at how easy it is to come up with a good work print on the first try, so long as your paper is the same. Changing papers will necessitate running new test strip prints to establish base times for that paper.
It's a little more time-consuming than a single exposure using a combination of M&Y filters, but it makes the tones more luminous, in my opinion, and is really easy and consistent. I've been doing it for years with excellent results. Les Maclean has some articles on this too. Our techniques may differ slightly, but essentially, we're doing the same thing.
Larry