Am I right to say that
1. if u press the shutter halfway it not only locks the focus but also the exposure?
2. if my foreground is dark and my background is bright but I want my focus to be on the foreground and exposure set to that of the background as I want the shot to be slightly underexposed so I can use shadow/highlights to bring out the darker details in the foreground in PS. If I were to set my exposure on the dark foreground that the lights in the backgrond would be blown and details are lost and no way to recover them.
So is the proper way to achieve this by first focusing on the background (depress shutter halfway), then use the exposure lock on my D50 to lock the exposure, then release finger from the shutter, recompose and focus on the foreground pressing the shutter halfway, and press the shutter with the exposure lock on?