Some good stuff here. I played with this a bit with nothing really special around the house today. So far it was fairly easy, can't wait to try it tomorrow.

I first noticed this when watching the documentary "war photographer", but couldn't get a grasp on exactly how he figured the exposures. So, this is a big help, and the answer to a question long on my mind.

Anyway I know nothing of Canon or Nikon, but with Minolta/Sony in manual mode, you can hold the AEL button and turn the command dial, and it automatically keeps the SS and aperture equivalent. If you turn the dial right, it opens up the lens, turn it left, it closes it and adjusts the shutter without effecting the exposure you previously set.