I am just a ''novice'' with exposure , wich seems a very complicated word yet to me.....but I foud of great interest all of what have been written by Ansel Adams on zone system..and shoting for dark zones (spot metering)as a way to extend the tone scal over 7 tones.. wich is usually what we get I guess...I am experience it these days..and try to shot to extend the scale..but i dod not fully understood the thing...;-)Hope it can help may be ;-)