-
focusing for portraiture
A person is more likely to move back and forth along the lens axis if their knees are parallel to the lens axis, and more so if they're seated. If you turn your subjects knees perpendicular to the lens axis, or nearly so, and have them turn their face towards the camera, you''ll have less focus problems. Standing subjects are far less likely to move out of focus, provided that they don't move their feet. Good luck.
Jay
-
focusing for portraiture
More light or faster film would be helpful in moving to a smaller f-stop.
Comfort is a huge factor in reducing squirming. Plant the sitter's elbows on the arms of a chair. Look into a posing bench. Or make one, yourself.
Traditionally, the only part of the face which MUST be sharp is the eyes. A little lens swing usually helps capture BOTH eyes.
But remember the old posing rules if you want a classy portrait. Show only one ear, or you will have a police mug shot instead.