[Frosty66]

Have given the MX a good clean , when I take out the viewfinder screen the "mirror" that is underneath it, I am not sure what it is made of and therefore not sure if it can be cleaned with anything. I have knocked/blown off the main dust but a few are more are stubborn. Can I treat it as glass and clean it accordingly or is it some delicate coating which should never be touched or directly cleaned , especially with fluid ?

[kb244]

Both the fresnel of the focus screen and the mirror are delicate, even a microfiber could scratch them. Best practices is contact less cleaning such as an air bulb.

Otherwise what he said about a sensor swab or similar cleaning designed for delicate surfaces as you don't want to use pressure that could grind any grit into the surface.

[kb244]

Aware of that, just noting it because some people try to clean the textured side of the focus screen itself removed. As you said the prism is more durable, I'm noting the spots that are not.

[Ranchu]

Don't clean it, just blow it off. Anything on the mirror is out of focus when you look through the camera, so you won't see it unless it's fogged or hazy. Maybe not even then. If you're worried about how it looks because you want to sell it, fine cleaning scratches on the mirror look just as bad if not worse than some specks or crap. It's nearly impossible not to leave any if the mirror needs such treatment. Again, it doesn't effect anything, and you can't see it.

[Frosty66]

Thanks all, so what is it actually made of ? the reflective surface is actually on the surface and not on the back of a glass is that correct, thats what it looks like.

[Ranchu]

The mirror is on the surface, correct. Early ones were glass, modern ones are plastic because it's lighter so the mirror can move back and forth more easily. I don't know for sure, but I'd assume it's plastic on the MX.

[cooltouch]

Given the MX's age, I'm inclined to think the mirror is glass. Heck, back when the MX appeared on the scene, eyeglasses were still made from glass! As for the substance, typically with back-silvered mirrors, they just use aluminum these days. For a front-silvered mirror, however, I don't know what they use.

On the subject of focusing screens -- something I picked up from a working pro back when I was first getting started in photography -- a quick tip for cleaning simple, one piece focusing screens. Handling the screen by the edges, drop it into a plastic film container. Add a couple of drops of dishwashing detergent. Fill with warm water. Seal the top of the container in place. Then shake well for a couple of minutes. Drain and flush until rinse water is clear, then, handling only by the edges, lay the screen down on a paper towel to dry. Blow it off with a puffer brush or whatever, then reinstall.

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Last edited by cooltouch; 04-06-2017 at 10:30 PM.

[Frosty66]

On the subject of focusing screens -- something I picked up from a working pro back when I was first getting started in photography -- a quick tip for cleaning simple, one piece focusing screens. Handling the screen by the edges, drop it into a plastic film container. Add a couple of drops of dishwashing detergent. Fill with warm water. Seal the top of the container in place. Then shake well for a couple of minutes. Drain and flush until rinse water is clear, then, handling only by the edges, lay the screen down on a paper towel to dry. Blow it off with a puffer brush or whatever, then reinstall.

Thanks I was thinking whether its better to take the screen out or leave it in when replacing the mirror dampers. I left it in and did get a bit of black gunge on it but it cleaned off relatively well and looks good through the viewfinder. A pain but obviously would have been worse if it wasnt there and the mirror behind it got black gunge on it. Nect time I am thinking of taking it out sticking masking tape to it and the putting it back before damper replacement. Would masking tape be too strong ? I could use the sticky bits of post it notes if it's that delicate I guess.

It's surprising how much better my light seal replacement went second time round once I'd learnt from my mistakes !

[Ranchu]

I always leave it in, there's all kinds of crevices crap can hide in under the screen, and be hard to get out, only to come out later. Cooltouch's guide to screen cleaning is good, I usually do a final rinse with distilled water and use coffee filters to set the screen down on while I dry my hands before blowing the screen off. I wouldn't put tape on the screen, but it works ok for removing shreds of the old bumper if that's what you mean..

[cooltouch]

Good idea on the distilled water and the coffee filters. Less of a chance of scaly residue and tiny bits of fiber detaching, methinks.

I ran into a situation once where the mirror bumper had turned to sludge and a previous owner had smeared it all over the focusing screen. It was in a Canon FTb, which doesn't have an easily removable screen (camera has to be dismantled to remove it). I used some solvent that I don't recall anymore what I used. Probably either alcohol or acetone -- most likely the latter. I do recall that it quickly dissolved the sticky sludge and I was able to wipe down the screen with a few gentle repetitions using Q-Tips until it was clean.

[Ranchu]

I destroyed a screen once by using alcohol on it, it frosted the surface. I think there are some plastics that can survive alcohol and some that won't, but I can't tell the difference. I would think acetone would dissolve all of them, but I've never tried it. If they're that dirty, or more commonly there's dirt behind the screen, I'll go through the top. Unless it's a spotmatic/K1000/KM. There's layers of foam down around the screen holder on those, and it's a PIA. I only did it once, that was enough. Often though, the dirt is just above the rectangular lens above the screen, and it's a lot easier to wipe off with a qtip and a blower. I use a magnifying glass to see the specks and dab them off with a dry qtip, unless I NEED to use liquid on the rectangular lens. Sometimes that's enough.

[Frosty66]

In the end I tried not putting anything on it first, a blower would not do it, the specks were a little too adhered to the mirror, but not by much, a slight touch with a dry Q tip and then a blower worked wonders. I can now hardly see a spec through the viewfinder. A slight abberation from where black from the damper was removed but TBH I probably only notice because I am looking for it.

On the bodies without interchangable screen, is it worth the effort trying to do the same ?