Hi, I got a friend who recently brought a Nikon Nikkor-S Auto 50mm f/1.4. When tested on site, the aperture ring seems to be fine, but after bringing it back, it seems a bit loose and shaky. I am wondering if there is a loose screw on the lens or something. Anyone with experience on the lens can advice. I search around online and all information I get is about Lens unable to mount on digital body without modification. BTW my friend lens isn't modded.