Changing Focusing Screens on Nikon SLR Cameras
When you look through the viewfinder of an SLR camera, the image you see is focused on the aptly named focusing screen. The standard screen that ships with Nikon cameras is called the "B" screen, but many landscape photographers switch to an "E" grid screen instead. This is the same thing as the regular one except that it has an added tic-tac-toe grid etched on it. Lining the horizon up with a grid line helps to avoid problems with crooked pictures. The only problem that remains is how to actually replace the screen.
First off, not all cameras have replaceable screens. Among current and recent models, all professional F-series and D-series bodies do, but the D50, D70s and D200 do not. At least some of the bodies that don't have on-demand electronic grid lines instead, so check your camera manual to find out what you need as well as what you already have.
If you buy an "E" screen for your camera, the first surprise you will encounter finding that it comes without any instructions at all. A check in your camera manual should relieve your anxiety somewhat. In my experience, they all contain at least a brief description of how to replace the focusing screen. The description tends to be somewhat lacking in specifics and the diagrams a bit small to answer all your questions.
Let's see if we can do better here.
You'll need a few tools to do this right, the most important of which is the special tweezers that come with the new screen. In addition, I'd recommend having a good blower such as Giottos Rocket, a headlamp or other good light source, and a magnifying glass or loupe.
Find a good, clean work area and lay out your tools. Take the special tweezers out of the package and practice picking up the new focus screen. If you must touch the screen with your fingers, do so by the edges only. The last thing you want is a fingerprint on the surface of your new focusing screen. When you're comfortable with the tweezers, put the screen back in its package.
New Nikon focusing screen and tweezers
Holding the screen with the tweezers
(Back side of screen shown to check for dust)
Next comes removing the old screen. At the bottom of this article is a diagram of what you should find inside your camera. The view is looking in and up towards the prism, with the screen halfway removed so you can see how things go together. When you open your own camera, the screen will be held in the screen frame and latched in the up position. Locate the screen frame latch and pull it towards you with the hooked end on the tweezers. Gravity should allow the frame to fall open, but if it doesn't, turn the camera upright and give it a gentle shake. The frame is spring-loaded and hinged at the back so the front should swing downward as shown in the illustration here. Once loose, you can use the tweezer end to open the frame the rest of the way if need be. It only needs to come down far enough to allow the focus screen to be removed. Remember that your camera's mirror is underneath the frame.
Next, locate the tab on the front edge of the focus screen and grasp it with the tweezers. Lift the old screen up and out of the camera body and take note of its orientation so you will be able to hold the new one the same way. Set the screen down on something clean. You may want to put it back at some point in the future, so take good care of it. When finished, you can put it back in the package the new one came in for safe keeping.
Pick up the new screen the same way you were holding the old one. Hold it up in good light and look at it closely to make sure it is clean. Use a magnifying glass to look at it closely. Even small specs of dust will be quite visible in the viewfinder if you miss them now. Unlike dust on your sensor, dust on the focusing screen won't affect picture quality since the mirror lifts up to completely block the viewfinder and screen when you the shutter fires. Big dust particles underneath the screen though can affect your ability to manually focus since they will prevent the screen from sitting in the correct focus point. The most effective way I've found to clean dust from a screen is a good strong blower. Even a clean microfiber cloth can leave an annoying amount of dust specks behind on a screen. These things seem to be dust magnets for some reason, so be slow and methodical if you find cleaning is necessary. A brand new screen shouldn't really be a problem though.
When you are satisfied that it is clean, gently place the new focusing screen in the open frame and check carefully that it is aligned correctly. You will have problems if it is crooked or not centered. You are performing a delicate operation here so don't rush.
To close the frame, pull the frame latch forward and swing the front of the frame up until it latches. Don't force it. If it doesn't latch easily, stop and inspect the alignment of all the components. The screen should be sitting evenly in the frame and the frame goes underneath (behind) the screen latch. An easy mistake is getting the frame on top of the latch, forcing the latch further down into the body. Again, take your time to be sure you get it right. The frame is very thin metal and can be bent out of shape if you force things. For some reason, the screen on my D2x is much more finicky than I remember it being on any other Nikon body I've owned. Doing this is not difficult if you are careful, but you do need to be careful.
Once the frame has been latched, check your work. If everything looks good, turn the camera on without a lens and set it to manual focus. Fire the shutter a number of times to make sure the mirror goes up and down correctly and that the screen doesn't pop out or anything. Sometimes the frame can seem to be latched when it really isn't so if something is wrong you would be better off finding out now than when you are out shooting.
Congratulations, you have now successfully replaced your focusing screen.
If you are one of the growing masses who have a digital SLR, this may be a good time to clean your sensor as well.
Update 9/30/2006 - While Nikon does not officially support changing the focusing screen in models such as the D50, D70/D70s and D200, users of such bodies might want to check out Katz Eye Optics.