This weekend, I pulled out my 85 to use and went to close the aperture and noticed it wasn't stopping down on my F3 while using the depth of field preview. I have examined it and basically, when you close the aperture ring, the notch on the back of the lens (on the mount) is not moving at all. Once the ring portion is closed, you can manually move that notch to adjust the aperture properly. Is there an easy fix for this or should I have a professional look at it?