Quote Originally Posted by AllenBaxter View Post
I have tried metering through the lens with the Hoya R72 filter and the meter does not appear to pick up any light. The filter is really opaque. How does the Hoya R72 filter differ from the Red 25A filter?
According to a Hoya brochure, a 25A filter passes light of wavelengths above about 600 nM which is well into the visible range. The R72 cuts off below 720 nM which is nearly out of the visible range. I have never shot IR film in a camera with a built in meter, so I have no experience to go on there. It seems possible to me that even if a light meter sensor has IR sensitivity, the maker might put some filtration over it to reduce sensitivity outside the visible range. (That's done with the sensors in d!git@l cameras.)

Based on my limited experience, I think Ron's exposure sounds a bit short, but in spite of the anti-bracket comments, I think a bit of it isn't a bad idea until you establish some sort of base line.