One of my longstanding interests is long exposure night photography.
However, many of the situations where I am shooting require exposure lengths on the order of 10 minutes, which is far beyond what the internal meter in my camera (5DII) can handle.
Right now, I take a test exposure, extrapolate from that to guess my exposure time, try again, etc...
This works, but since the test exposure alone can be 10 minutes, and it generally takes me a few shots to get the exposure right, it can take 30 minutes to an hour just to figure out exactly how long I need to expose for.
Obviously, this is really inconvenient (fortunately, long exposure subjects don't move much, most of the time).
For instance, recently I did a series of 13 minute exposures at f4, ISO125. It came out really well, but I would up spending 2 hours to get one shot.
Anyways, is there an easier way to determine how long an exposure has to be, preferably that doesn't take multiple test exposures? I've looked at light meters, but none of them make explicit statements about how low a level of light they can handle.