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Old Jun 23, 2012, 1:04 PM   #1
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Default Dust in Camera, But Not in Sensor

I change between lenses a lot, and recently I noticed a hair and a large piece of dust whenever I look through my viewfinder. I don't think the dust is on my sensor because it never affects my photos, but it DOES affect my ability to automatically focus. It appears that the dust "confuses" the auto focus, which is super annoying when I just want to take a simple photo. Does anyone know where this dust could be in my camera, and if so, how to clean it? I know it's somewhere on my camera, not my lens, because it's still there when I change lenses.

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Old Jun 23, 2012, 3:08 PM   #2
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Look on the mirror.
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Old Jun 23, 2012, 4:18 PM   #3
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G'day CP

Dust visible in the viewfinder is very common - and contrary to philby above, it is -not- on the mirror ... the mirror is never in focus so you will never see it unless it is a "real-big-problem"

Firstly - never-never-never-never touch the mirror surface
The mirror is front silvered with no protection from scratching - and any touch from any cleaning brush will look like sandpaper has gone across it

1- remove the lens & turn your camera upside down
2- look at the underside of the viewing screen
3a- if there is dust visible, get a "000" sized 'camel-hair-artist's-brush' [about 2mm diameter & very -very soft] and carefully wipe the dust off the viewing screen ... OR
3b- purchase a device called a 'pocket-rocket-blower' where you squeeze the blower to give a burst of air across the viewing screen

nb- it is possible to carefully lift the mirror mechanism up till it covers the viewing screen [it moves freely & won't break] so that you can clean under it ... tho be careful of the electronics you see under the mirror

Regards, Phil
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Old Jun 23, 2012, 4:56 PM   #4
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If the dust you're seeing is messing with the AF system, it could actually be on the mirror. The mirror which reflects light up to the focusing screen and the optical viewfinder is only semi-silvered. Some light passes through that mirror to a second mirror that reflects the light down to the phase detect AF system in the base of the camera body. If you're seeing it AND it's messing with the AF, the only place it can be is on the mirror.
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Old Jun 25, 2012, 9:31 AM   #5
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One other point don't touch the focusing screen face even with a brush.
Been there, done that, and have damaged 2 focusing screens by touching them with a cleaning brush. On my bodies the focusing screen is a 65$ user replacement piece, other bodies need to be sent in for a much more expensive repair if it needs replacing.

A blower like the Giottos rocket is OK, to try to puff the offending bits off.

IMHO: if it is visible in the viewfinder but not actually affecting the image or camera operation, leave it alone!

Imaging is all about light and your ability to sculpt it.
Equipment is just a secondary nuisance.

Last edited by PeterP; Jun 25, 2012 at 9:34 AM.
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Old Jun 26, 2012, 1:41 PM   #6
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Thank you for all your input, it's really helpful. I'm going to buy a rocket blower online, and I saw the GiotoBair blower that came with a kit; should I get that?
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Old Jul 28, 2012, 9:33 AM   #7
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I just had that problem on my D70. There was dust on the mirror and on the sensor. I bought a Rocket-Air, locked the mirror up and blew away the pesky dust in my viewfinder. I also cleaned some specks on my sensor and I'm really happy how it worked out.
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