E.g., yesterday I wanted to do an ambient exposure of a wildflower. Got 1/2 second (f/16 + 2.5 stops bellows) Velvia 50. That's plenty enough to overpower ambient with 4 stops to 1/30, though that was overcast skies.

I was going to try a flash exposure two stops from ambient but it started raining on me and I had to get the beast packed away. I don't like shooting those black background type flash shots.

Its true I'm screwed in sunny f/16 conditions but I would sooner shoot ambient with a diffuser for a macro shot in those conditions.