Originally posted by vonBaloney 
All my attempts to ever clean a focusing screen beyond using a rocket blower have damaged it. (And don't blow it with canned air either -- it can fog it if you get any of that cold mist.)
I have removed dry crumbs with a camera repairman's cotton bud (not the same as a Q-tip) by a simple touch to the crumb. It was a two handed operation and I would not recommend unless you have steady hands and magnification. Beyond what can be done with a rocket blower, a thorough cleaning requires taking the screen out. With the XR7, the means partial disassembly (removal of top plate, some ribbon connectors, and the pentaprism) to gain access to the focus screen.
Once out, actual cleaning is not difficult. Here is what my tech guy* does. A few drops of dishwashing soap (Dawn, Palmolive, or similar) in distilled water using gentle finger action on the screen surface. Rinse well with distilled water and allow the water to drain off. Blot the edges with an absorbent cloth and use a rocket blower to disperse any droplets that may have formed.
Katz Eye Optics provides these instructions:
Quote: If your screen has become extremely contaminated, such as with fingerprints, oils, or some other foreign contaminant, you have a few options. First, it is possible to wash the screen, if appropriate precautions are taken. Avoid this if at all possible, but if you have serious dirt or oil that won’t respond to the gentler methods, here is the appropriate procedure. Get a very soft artist’s brush – red sable works well. Wet the screen with warm tap water; place a drop of liquid dish soap (like Dawn) directly on the screen. Wet the brush and work the soap thoroughly into the screen. On the matte (prism) side, you can use any motion you’d like. On the other side, there is a Fresnel lens that has a series of concentric grooves; to clean them properly, you will need to work in circles starting at the middle and getting progressively larger. When you’re done, rinse thoroughly in warm water using the brush to help to soap get off. Then, follow with another thorough rinse, this time in dead cold water. Finally, blow the water off the screen with canned air (making sure not to freeze it) or a big bulb blower (like a rocket blower). The key is to blow the water off the screen before it can evaporate and leave water spots. Distilled or de-ionized water will be less prone to leaving water spots and should be used as a final rinse, before drying, if it is available.
I suspect ultrasonic cleaning in mild dish soap might also work well.
Steve
* Mike Knight at Knight Camera in Vancouver, WA USA
) make it worse
Post #2 by vonBaloney
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