I got a Keystone Executive K51 16mm movie camera from a friend. I'm familiar with vintage analog still cameras but have yet to use a movie camera. I'm eager to put it to use and I was checking out the features, but I can't seem to figure out how to focus this camera. There is no focusing ring on the lens, nor is there any indication of distance settings from the subject. The top of the camera has 3 settings for wide angle and telephoto, which changes the view in the viewfinder. Maybe this is the key to my concerns?! Does anyone have experience with this camera? I do not own the manual and there is no manual online.