Quote Originally Posted by AgX View Post
Luminance = "Brightness" of your subject (in this case the reflection from your chamber wall.

For proper working of that meter you need a mercury battery. Have you got one??
(Or a well made electronic substitute?)

No, one more thing to buy...
Right now with digital I am shooting at ISO 100, f.10 and 1h30m
if the meter only gives 1hour, with ISO/ASA 100 it would probably give f5...no?