When the Canon EF 50mm 1.4 USM lens is dropped or impact damaged in any way, it usually causes the auto focus and/or manual focus to not work properly.  It will either limit focus movement or not allow focus at all.  I can repair this problem.  The focus cam barrel has to be removed to straighten where the bend has occurred.  To prevent this from occurring, install the original lens hood. Any impact to the front lens barrel will transfer the energy to the lens hood, not the focus mechanism.  Check out my Ebay ad at    http://www.ebay.com/itm/Canon-EF-50mm-1-4-USM-lens-repair-/322403410650