Inspired by posts by Joseph Wisniewski (here and here), and by the big nasty scratch I put in my screen trying to clean it, I decided to try replacing the focusing screen in my D70. I'm pretty pleased with the results, and would like to add a couple of comments and suggestions to what has already been said. To remove the screen, take a cheap miniature slotted screwdriver and grind or file a notch across the tip to fit over the wire bail. That will keep it from slipping off. If I'd done that at first, I wouldn't have had to replace mine at all. I chose a "J" screen from an N8008. It has a microprism area but no split-image, which is how I like it. I note in passing that the edges of the split-image area on a K3 screen stick up enough that they will probably press against the LCD screen, which may not be a good thing. I cut my screen to 0.800" x 1.000", give or take about 3/1000 plus half an inch slop in my cheap calipers. Anyway, it fit fine. By my measurements, the center of the viewfinder is about 0.335" down from the top, 0.465" from the bottom of the screen, where "top" means the edge near the focal plane and "bottom" the edge near the lens mount. (Incidentally, that's backwards optically, but matches the way you hold the screen when you're putting it in.) Note that you'll only take a couple of hundredths off the bottom of the screen. I started by putting a piece of transparent packing tape over both sides of the screen. That way I didn't have to be very careful handling it. I used an X-Acto knife to trim the tape away from the edges of the screen, then measured and cut one edge at a time. If you fully finish each edge before going on to the next, you always have a good reference edge at the other side to measure against. I cut each edge roughly with an X-Acto razor saw, which is a miniature saw with a rigid blade designed for model making. I finished the edges on hobby sanding film--fine sandpaper with a plastic base. Try to be as exact as you can finishing the sides, as it turns out to be really annoying if the screen is off-center horizontally. (Luckily, I'd figured on screwing up once, so I had two screens and got it right the second time.) I don't know if it's possible to get the screen perfectly centered vertically on the first try. I was able to trim it a little more on sanding film until it centered up right. If the center ends up low, you'll have to take some off the "bottom" (optical top) of the screen. Then when you drop the screen into the camera, you'll have to turn the whole thing upside-down and tilt it so that the screen slides forward before clipping down the bail. The bail is tight enough that the screen won't slide around after that, though I don't know what time and vibration will do to it. The screen I used works quite well. Focus by eyeball matches up with automatic focus and the electronic rangefinder with no discernable difference.