Can you be a bit more specific in what you mean by vertical play? The focus lock would prevent the standard from moving forward or backward of course. I gather that when the focus knob is locked that the camera does not move when the holder is inserted, and everything is in focus. Consequently one suspects that everything is in order. However, once more, Michael A. Smith is certainly the expert in all aspect of the KMV camera. Hopefully he will be able to answer your question..