Rich, I've discussed (spouted, nay, hollered even) about the F3 screens in F4 bodies. It can be done ONLY if you dismantle the F3 screen from the frame and place it As Is into the empty F4 screen frame. Its the imperceptible differences in the frames that Will cause focus errors. BUT IMO unless you absolute need a screen that you either can't find or something that wasn't offered (the H series) its best to stick with the F4 screens. The Red Dot F3 screens use nearly the same if not the exact screen material preparation so the brightness is the same or nearly so. The Non-Red Dot F3 screens are noticeably less bright, but do have a nice contrast. Its my understanding that Nikon changed to the Red Dot design to Upgrade the F3 during the mid to late 1980's as the F4 and N8008 came out with the improved screens. Both the F3 and F4 have screens that are the same designations except the F4 does not have the H series, again its my understanding that the Matrix metering (using the DP-20) had problems with the full microprism surface. Pity tho', the H series was my Secret Weapon to sharp low light sports photos in the 80's and 90's at the newspaper I worked at. Now I must have 25 screens for the F3 and F4! The B, the J and the U get the most use.