I have an older "chrome knob" 35/2.8, and it definitely is adjustable. At the end of the knob is a little spanner nut, which is a jam nut that adjusts play on the knob. For mine (which was also loose when I bought it in "bargain" condition) I milled or filed a 4 millimeter 1/4 inch socket into a spanner.
On that one (and it appears similar in the drawing above for yours) if you loosen the spanner nut, then tighten the knob clockwise and then retighten the spanner while holding the knob, it should tighten up. Because there's a little thread slop to take up here, it may take a couple of tries to get the tension just as you like it.
e.t.a. I note that the knob on the newer lens has a cap on it, which I suspect you must pry off. Mine is exposed, and the adjustment is pretty obvious.