Perhaps there is no difference between digital noise caused by longer exposures and by high ISOs - one would think so based on camera reviews which report only on the latter. (Perhaps there are some exceptions.) However the noise doesn't look the same to me.
I've been experimenting with medium long exposure shots (1/2 to 4 seconds as a rule), which naturally use the lowest ISOs, plus neutral density or polarizing filters (or both) and small apertures. I'd not had problems, naturally, with my old Nikon F3 and film and I had not had problems with my Oly E-330. However, the 330 is in the shop under warranty as it lost its red channel. (Apparently this is not unknown; I might add that I still really like it and await the E2/E3 eagerly.) As a result I've had some good results with my older E-300, but for some pretty bad noise issues. Some of the shots I consider too bad to fix manually, at least I'd rather not, even though this kind of noise lends itself to manual fixing as it's like blown pixels. I don't like the noise filters in CS2 and I don't own any dedicated noise cleanup software. Therefore I am asking for advice. Especially with this kind of noise, what packages have been helpful? Alternatively, is there really nothing for it but to go in and do them manually? (There are only a handful that I do not want to do that way.) Thanks.