Alright. I use a Canon Rebel Xt. Lets say I set my camera up on a Tripod and use a cable release. Lets say I'm using a few filters, one of of them is an ND8 circular filter, at f/22, ISO 100... I'm shooting in Manual because even at thirty-seconds the image was too underexposed.. so, my question: How do I know how long to leave the shutter open for? A minute? A half-hour? An hour? How does a photographer know? And lets say I had 15 minutes to figure it out before the sun went down, or some other scenario. Is there some device that tells me how long to keep my shutter open given the lighting conditions, other than the camera's built in meter (which finally hits 'bulb' as a last resort)? I refuse to believe its just a guess game. *sets up equipment "Lets guess 15 minutes" "okay that was too dark, lets guess 30 minutes" "that was too dark.. *45 minutes waisted* - lets try an hour"