Kodak T-Max films are sensitive to a little past 700 nm; the same is true of Fortepan, if you can still find any. Ilford SFX is probably the best for H-alpha of the films currently manufactured; it's sensitive to about 750 nm (and fully panchromatic, unlike most true-IR films of the past). Rollei IR 400 (made by Efke, a 400 speed daylight rated version of their IR820) is sensitive further out than SFX, but it's a *lot* more expensive.
All of these films are a lot slower with the H-alpha filter than they would be without a filter, but that's to be expected; you're blocking off most of the light they can normally record.
For night sky, it's tempting to suggest one of the Fuji slide films -- IIRC, it's Velvia that requires no reciprocity correction to something like two hours (making it the fastest color film you can load for very dim light).
Bookmarks