a bit confused here about the ISO setting to use with the Cokin P007 filter, as almost all I've read says ISO 25 with this film.
I am ok with bracketing on roll film, but would like a starting point more in the ballpark
Shooting it on 35mm (Kodak Retina IIIC) I did a roll with every shot at both 25 and 12, with a no-name Chinese R720 filter. Both seemed reasonably dense, but I found the 12 overall closter to where I like it. I haven't tried it at lower EI or on 4x5 though. The camera was recently CLA'd so I have every reason to expect the shutter speed was moderately accurate.
Back when I was shooting IR the consensus was that the filter required 10 stops - that would put Rollei 400IR at ISO 3. But ISO 6 sounds familiar. What I would recommend is taking 4 test shots in the same light at ISO's 3, 6, 12, and 25 and see which one gives the result you are looking for.
Thomas
Some online research, and my own crude test, indicates that the filter takes about 6-6.5 stops off the reading.
So it is with my filter. Other 720nm filters may block more or less. It's a wild world out there.
Well, it depends a lot on exactly which filter you use and the environment in which you shoot. Also, some of us have different metering habits. Try a test roll with bracketing and then you will know what setting work for your exposure and development process. BTW, I'm using HC-110 "B" for my work. ISO 25 seems pretty unlikely, though.
Hoya R72 seems to be about 6 stops from my testing.
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