Don't just focus (
) on how close you can focus a lens, like the S-Planars or Makro-Planars. Also consider what the sitter will look like when being so close to him or her.
I you want to "
have someone's head take up more than the entire frame", 120 mm and 135 mm lenses are way too short.
The field of view you are then after measures about 150 mm square.
Using an 120 mm lens, the focussing distance (film to subject) will be not even 600 mm, the subject distance about 440 mm, the front lens to subject distance not even 400 mm. A 135 mm lens is not much better.
Even when using a 150 mm lens, the front lens wil not even be 550 mm away from your subject.
(Of all these lenses, only the 135 mm on the bellows will reach close enough without aid of extension tubes.)
Much too close to worry about whether you need a softar or not. With a tack sharp lens, or a lens that is toned down using softeners, the sitter will look groteskly misformed from these distances. If only faces were flat...
A 180 mm lens is beginning to get you somewhere, but still not quite far away enough to get better perspective. A 250 mm lens takes you back to a focussing distance of (only!) about 1300 mm, front lens to subject distance of still only 970 mm (who thought you need a big studio when using a lens of this length?
)
It will take some serious extension (about 62 mm extra, above what the lens brings along itself) and 1.5 stops more exposure. But it will create a good picture.
P.S.
If you want to have a look at what you can do with these lenses, play around with the online Close-Up Calculator you can find
here.