I use a focal length 0f 80mm as the default on most of the cameras. For a Poser portrate I think somwhere between 80mm and 110mm is best, (just my personal taste). Actually it is the point of view which is the important thing, this determins the perspective amongst other things. I don't like Posers habit of changing the scale of the camera when the focal length is changed, so I locked the scale channel on most of my cameras by editing the preferredState.pz3, using "forceLimits 4" and setting "min 1" and "max 1". I also added an extra Dolly Camera and 2 extra Aux cameras to the preferredState.pz3. I sometimes parent a Poser square to a camera and apply a transmap for a vignette effect.