Originally posted by swestin 10 stops? How can you see to frame & focus with only 1/1000 of the light coming through?
As a standard approach, you'd first compose and focus, then screw on the filter, and then compute shutter speed (I use an app or just count). And also have a viewfinder cover on to prevent reflections coming in through the viewfinder. Live view in bright sunlight can help with focusing and composition (though it's noisy when punched in), but for metering over 30s you'd need to calculate exposure time.
And yes, it's so dark that I don't find it practical for anything except during daytime, close to sunset or sunrise it's still far too dark for how long I can wait around