The elmar 50 f2.8 collapsible lens I have feels a bit loose, where the entire collapsible part of the barrel would drop back and forth if I just tilt it. I don't know if this is the norm for this lens, my other summitar and thread mount elmar 5cm f3.5 don't have this problem. It still locks in place and functionally works well, just quite annoying. I wonder if there is way to adjust this?