Both cameras have interchangeable focusing screens. The FE2 takes K, B and E screens - combination split image/microprism, plain matte, grid. Using a lens like the 300/4.5 with the K screen will be acceptable in bright light and when the subject is easy to make out from its surroundings. If this is not the case then an E screen can make things easier and can also aid in composition. The correct E screen for an FE2 is the E2. If you use the E screen from the FE or the E3 screen from the FM3A you will need to adjust your exposure. The F3 will give you a lot more choices when it comes to focusing screens but the E is still a good choice. In lower light you can find that the top or bottom of the split image section of the FE2's K screen wil black out if your eye is not perfectly centered. The E screen has no focusing aid in the center to black out. You might find that the E screens are also handy for macro work and for using slower zooms.