There is 'unofficial' information that the whole of the production facility will be closed as film is not enough to keep them going on it's own - basically they don't own the land (rental costs etc.) so the fixed-costs of the operation wouldn't reduce with the reduction in production. The end of the paper-line may be the end of Fotokemika too, unless there is some tiny vestige producing chemicals. See the other thread here, the one on RFF etc. etc.
Back to the original question:
If you want to darken reds, any filter that doesn't pass red will do the job. A sharp-cut green or blue filter will do the job, but have different effects on other colors in the scene.
I'd start by using some of the more common blue and green filters; the 44 filters are getting harder and harder to find and, as far as I know, are now only available as Wratten gels. The B+W 081 and 080 seem to no longer be available. I've been trolling for one in 67mm size for some years now and can't seem to find one.
I do have 44 and 44a filters, which I use for approximating the look of orthochromatic film using regular pan film. I also use an 80B for this from time to time with good results. It passes some red, but does darken it quite a bit. If you've got one of these laying around, you might give it a try.
It's definitely true that the Wratten 44, 44A, B+W 080 and 081, and other cyan filters are extremely rare in the US, and have been for a very long time, at least since the 70's in my experience. That's one reason I purchased mine in Germany in '82.
I did see yesterday that Calumet has a 40 or 50 cyan CC filter in a square plastic filter, and the 80A and 80B may be the best chance these days, but even those are becoming rare in the days of digital specification of color temperature. After posting, I noticed that at least in the US, dealers are now listing the B+W 080 and 081 as discontinued (the place I normally look was offline when I posted). Sometimes that means 'no longer made', sometimes 'no longer imported' by the distributor. I'd suggest that anyone looking for any kind of minus-red function in a filter search thoroughly now and buy now.
Thanks for the help folks. I guess this is why I've had trouble finding this. So, if I don't want to also darken blue sky in the image, I would use Wratten 44, 44A, or B+W 080 or 081, correct? Not green.
Don't you guys have any luck on auction sites for stuff like this, or not? I'll be looking myself so one more to compete with. Thanks.
If you can't tolerate an alteration of blue sky then I think you are correct. I've never been that constrained.
Have you thought about calling the folks at Lee Filters and asking them what they recommend and can supply? They have a cool feature on their website that shows their offerings and the spectral characteristics. Or calling Rosco? I've used Rosco gels as filters and while not ideal that works too... and inexpensively.
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Good idea, Brian. This is a very special use, and a cheap gel might work
additive vs. subtractive color
White = Red + Green + Blue. Using algebra, White - Red = Green + Blue. We call Green + Blue "cyan." So a cyan filter is indeed "Minus Red" and should pass green and blue mostly unaltered but block the red.
Reversal film works in exactly this "minus red, minus green, and minus blue" fashion. The red-sensitive layer contains cyan dye couplers, the green-sensitive layer contains magenta dye couplers, and the blue-sensitive layer contains yellow dye couplers. When the developing process is complete, there is cyan dye where the red light wasn't, magenta dye where the green light wasn't, and yellow dye where the blue light wasn't.
Shoot more film.
There are eight ways to put a slide into a projector tray. Seven of them are wrong.