Cool idea but not practical especially if you value fine color correction. An accomplished color printer will oftentimes tweak the balance a 1/4 cc or even less. Once moved, attempting to reset the dials will leave you with a ever so slightly different color pack. This is only really an issue if the printer is trying to achieve consistent color throughout a group of images.
You're much better off dodging with cc filters. If you reduce the exposure then simply burn it back in with a filter over a burn card.
Unless there is mixed lighting it has been my experience that when I have a color cast anywhere it is actually everywhere. In those cases I've normally misjudged and once i got the correction right, what I thought was fine was obviously off too.
Mark Barendt, Beaverton, OR
"We do not see things the way they are. We see things the way we are." Anaïs Nin
Frotog - cc filters aren't even mfg to those tolerances. You're dreaming. You'd be far outside the range of a what a good colorhead can do anyway. A push of a button and I can go between presets. Plus you'd be putting something in the lightpath not really designed for over-the-lens use. Lighting gels are not made to the same standards as optical gels, which would cost a small fortune in anything large enough to burn with, and would still degrade the image slightly.
Presets? Are you using a computer controlled closed loop head? Regardless, you've completely misunderstood my point.The mfg. tolerances of dichroic filters has no bearing on my comment. Traditional color heads have analogue controls DREW. That means stepless control in dialing in the color pack. There are no definitive, calibrated increments.
OK, so the light beam goes thru about one inch or so of graduated overlapping subtractive filters with a
range of maybe 175 cc's. No gearing or dial on conventional equip is going to give incremental control
on such a small surface as you imagine, but you should be able to dial it in with less than a 5cc error. With a very sophiticated feedback colorhead like I use, one can sustain control within about 1cc. Gels (at least the ones I've measured on a densitometer) are often plus/minus around 4 cc's or worse. The pale ones tend to be far worse. But I have no trouble switching filtration even on my old Chromega additive colorhead in the dark, like for split printing. Keypads are nicer, but still no big deal. I've done a few experimental color prints this way, but if I really had to correct a print I'd resort to selective pan film masking of the neg, but that's another story. And the Fauxtoshop crowd have their own way of doing it, but most of them probably don't even notice green faces.
The only way to settle this is that I send the original negative to each of you , and see who returns the best print... just kidding. The real beauty of this is that I think you are both right.
I take out of this that there is many different procedures and lots of different equipment that I don't have. I agree with putting filters under the lens in the lightpath may cause image degradation (particularly with used ones in eBay) nor can I invest the money in sophisticated tools so I have to do with regular enlarger. So I will probably try both approaches somehow with the tools I have and see which one works best for me.
I'll sell you one of my enlargers if you want to try my method, Frotog ... that would at least buy me a
modest vacation cabin or new car, and I'd still have several enlargers left over. You're utterly out of you're league with that comment ...