i often times have taken portraits with whatever camera i am using on a tripod
( dslr, 35mm, 120 tlr, 4x5 and 5x7 ) have it prefocused, pre framed and
ready with a release just as you described. it is a great way to work with a subject
and while you converse with them, they almost forget the camera is there.
i trained with a portrait photographer who herself was trained in the 20s/ 30s
and she too used this for in-studio head shots and karsh esque portriats ...
it seems that a lot of people when they make portraits don't really interact with their subjects
they let the subject kind of do what they want, and capture what they see ... others dance with their subjects
and the portrait is a result of the interaction between the two of them ...[/QUOTE
You make a very important point here John I.M.O, too many novice portrait photographers approach portraiture as if it's still life, or landscape and instead of interacting with them and producing pictures that have a spark of intelligence and interest in their sitters expressions and eyes instead of one of boredom, and the hope that the ordeal will soon be over.