Quote Originally Posted by Cor View Post
... AFAIK was the MACO film made by EFKE, they used "normal" pan film (100 asa) and "doped" it with an IR sensitive dye, so that's why it needs heavier filtering that HIE resulting in very low speed.
That the MACO IR 820c was a "normal" emulsion doped with a IR sensitiser may be correct, but I don't think the conclusion necessarily follows. HIE has a lot more "deep IR" sensitivity, making IR a larger proportion of the light registering on the film. A "near IR" film like the MACO will need heavier filtering and give less (relative) sensitivity due to a different sensitising dye.