I plan to shoot some star trail shots in Death Valley later this week and have had little success in researching exposure details. I plan to do long exposures (1hr or more) and can find little technical info on issues of fogging.

I've read that because of the relatively slow lenses on LF cameras that fast films (400 ISO or more) are recommended. However is it not true that faster films fog sooner, I've also seen recommendations for using a medium speed film (200 or 100 ISO) but this was for a 35mm situation.

Does anyone have technical advice/experience with fogging and long expos? Has anyone had experience with say 6hr exposures re: fogging? Are smaller apertures (f5.6 or f8) a better idea on such long expos to reduce fogging, and does using a smaller aperture increase the time that one can expose w/o fogging?

Thanks in advance

John