Most portrait photographers that use a tripod aren't looking in the viewfinder when they trip the shutter. However the magic doesn't last more than millisecond, and you still don't know how great it was until you see it on film. The reason that movie makers and some photographer "tested" their subject/actors was to see if they had that magic. It may appear in the viewfinder and not on the film and vise versa.Originally Posted by David H. Bebbington
Also I photograph a lot of kids. That expression can change in a heartbeat. I can have frames less than a second apart that are nuanced very differently.