Fingermark on mirror/sensor/other bit

Ewan

Ewan

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Don't ask how, but I've managed to get a fingermark on something inside the camera. I can see it in the viewfinder quite clearly but it doesn't seem to be appearing on the photos, and with my (very) limited knowledge of how an SLR works that makes me think it's on the mirror. Now this wouldn't be a problem, accept it's right over the centre AF point, and it seems to be effecting the autofocus. If I point the camera at a scene that is not very contrasty, for example a misty mountain (lots of them in Scotland :lol:) it will not autofocus with the centre AF point but if I switch to any of the others it autofocuses instantly.

So do you guys think it is on the mirror and if so how would I go about getting rid of it?

Thanks,

Ewan
 
It could be on the mirror or on the focusing screen at the top of the mirror box.

How to get rid of it depends on whether it's loose or stuck on. For anything loose, I'd recommend a very soft brush such as Daler-Rowney SY21, which you can get from art shops or mail-order. It has very fine nylon bristles which won't scratch anything, and you can also use it for sensor cleaning. (You should wash it first in dishwashing liquid, rinse thoroughly under the tap and then allow to air dry - takes a few hours.)

To get to front part of the focusing screen, it's handy to have a brush with the ferrule bent at 90 degrees. Take care not to scratch anything with the metal ferrule.

If the crud is stuck on, you may need to use something like isopropyl alcohol (IPA) and a PecPad or microfibre cloth. Be very gentle though, because it's easy to damage the silvering on the mirror.
 
Thanks for that :). I already have what I think is a microfibre cloth but I'm not sure. It came free from a film-rental company and is meant for cleaning DVDs. I haven't used this though for fear of damaging it. I think it's quite a light mark so I'll look up that brush you mentioned.
 
Here is my thread where I've been asking the same questions...

There a couple of links there, including mine which leads to a cleaning kit (for beginners). They are around £25 but come with everything (apart from a rocket blower).

Take a look, it may be of some use. :)
 
Of course it could be on the viewfinder glass.... thats the easiest place to get a finger mark.

If its on the mirror, I have always cleaned mine with lens fluid [these days on a pecpad]. Never caused any problems, as long as you are gentle and as usual, only damp, not wet - I dunno, Maybe thats wrong, but I tend to think that the mirror is just another piece of your cameras glass and should be treated with the same respect and methods as any other. :shrug:
 
Lens cleaning fluid is usually isopropyl alcohol and that's fine. The mirror is silvered on the top and it is easier to damage the coating than a normal lens or filter, but it's OK if you're gentle. :)

A blower (like the Giottos Rocket) may help but I'm always concerned about it just blowing the dirt somewhere else. Please don't use 'canned air' because the propellants can leave a residue, and there is also the possibility of thermal shock because the air leaving the nozzle is very cold.

The cleaning kits are often expensive and you don't really have to pay much for what you need. The same goes for 'sensor cleaning brushes' - the Daler-Rowney SY21 does the job very well and costs about £3. :)
 
OH, that actually reminds me.... the D70s [could be on 200 too, I just happen to have the 70 sat here] - does it have some kind of double mirror mechanism? Under the main mirror, is a secondary small one, with what would seem to be a unsilvered hole in main mirror where this little one sits underneath it.... can anyone explain it? :shrug: Never really looked that closely before, but spooted it a week or two ago, and meant to ask how this all works.
 
Yes, there's a secondary mirror that is part of the autofocus system. Usually though it's the main mirror and the focusing screen that collect the dust.
 
Ahaaa! thankyou! :D I generally find that the worse dust [and this is relative, it isnt that much] is on the focusing screen, pressumably because the mirror throws it up there every time the shutter is operated, so a good blower is always a cheap and useful piece of kit to have.
 
You should be able to see a fingerprint on the mirror and I doubt it would show in the viewfinder. My gut guess is it's on the focusing screen. Have you had the screen out at some stage?

The screen is smooth on the inside surface (the one you can't get at) but a textured ground glass surface on the mirror side, It's easy to polish a mark off the smooth side, but the textured side is a different matter - you need to be very careful or you can make a real mess!

My honest advice is live with it or get it professionally cleaned.

Be careful with the mirror too - unlike conventional mirrors, they're often mirrored on the surface and it's easy to permanently mark them.
 
Thankyou everyone for your advice. Maybe this isn't quite as scary as I thought it was.

CT said:
My honest advice is live with it or get it professionally cleaned.
Click to expand...

My thoughts exactly, CT. I guess it might be cheaper to clean it myself but I'm a wimp and I'm scared of damaging something (can't afford another body for a long while).

What I don't get is why there isn't some kind of door that closes across the lens mount when you take a lens off. This would surely prevent the sensor/mirror/focusing screen from getting dusty/damaged?

I'm going to look at getting it cleaned, and see how much I'm gonna have to pay. Thanks again everyone for your help :)
 
Unfortunately, I have this strong suspicion that some of the crud comes from the mirror/shutter mechanism itself, especially when the camera is new(ish).

My 30D needed regular cleaning for the first few months, and some of the 'dust' looked like tiny oil droplets. I can't think what that could be except the residue from shutter/mirror lubrication. After a while it improved....

.... and the shutter seized. :lol: (Only joking.)
 
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