The way to set the focus screen is to put the camera on a tripod, with a piece of groundglass at the film plane. Focus the lens, on the filmplane (shutter open!) on an object at infinity - that is, a mile or so away. Then, without touching anything else, close the shutter and adjust the viewfinder screen until it's focus coincides with the focus at the filmplane. Double and triple check before you button it up.