Just tried this. Bought a 'P' type screen for F3, took it out of the frame and installed it in an F4 screen frame. (Damn little screws...) Put it in the F4, mounted several different lenses. Infinity focus is dead-on; focus at shorter distances agrees with the 'green dot' electronic rangefinder exactly. I had read so much on the Internet about how this wouldn't work, and some about how it would, so I risked ten dollars and tried it. Consider that a new 'P' screen for the F4 costs about USD 100 or more on eBay or other sites. It is SO nice to have a split image and a microprism focusing aid! Exposure seems perfect as well without any compensation.