ok, this is some of the fact: jeng,jeng,jenggggggg..
" nineteenth-century photographic material were nowhere near as light sensitive as today 's films. This mean instead of the fractional second exposure we take for granted, the pioneer photographers needed several minutes to properly set an image on a sensitised plate. while the shutter was open.(the first camera had no shutter. a cap was placed over the lens and the photographers would remove it to begin the exposure and replace it when the time was up.) Holding a smile for that length of time can be uncomfortable; that why they seen the same sombre look on early portraits. That's what a relaxed face look like".
hhaha... this is good, so then. we are lucky because don't have camera that not wait for a long period for a exposure. huh.. don't believe me? here some fact:
'a good portraitist will not ask subject to smile and have them hold it even for more than a few secong, as the smile start looking force. With the long exposure of old, the smiles would look phony and detract from the photo. Look at your in the mirror with a 30-second smile on your self '.
now, believe it? huhu...