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08-25-2010, 09:52 PM   #1
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Dust Alert false positive?

Ok, i took my lens off today just to show someone the mirror, bad idea. I then got dust on my sensor, black spots on my photos, cant see on viewfinder, ect...

I ran Dust Alert and it showed MANY black specks, and one big splotch that definitely was not dust, i was worried because i thought some splash of moisture of some kind got onto the sensor.

I got home did dust alert once more, and the splotch was still there, so i set the camera on cleaning mode, blew off the sensor with a Giotto Q-Ball and ran the Dust Alert again. All of the black specs were gone, but the splotch was still there. I took some photos and there was nothing wrong with them, they looked fine, no splotch at all.

I ran Dust Alert 2 more times and after the second time the splotch stopped showing up.

What happened?

08-25-2010, 09:58 PM   #2
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What were you pointing your camera at when taking the dust alert photo? What sort of light source?
08-25-2010, 10:02 PM   #3
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QuoteOriginally posted by goddo31 Quote
What were you pointing your camera at when taking the dust alert photo? What sort of light source?
Just pointing it at a well lit blank white wall. I tried some more Dust Alerts and the splotch has not returned, seems to be gone for good, but i would still wonder why this showed up in the first place
08-25-2010, 10:12 PM   #4
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Put your cap on lens then Dust Alert.

08-25-2010, 10:40 PM   #5
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QuoteOriginally posted by Danny Delcambre Quote
Put your cap on lens then Dust Alert.
Direct from the instructions:

From page 286

Fully display a white wall or uniformly bright subject in the viewfinder and press the shutter release button fully
08-25-2010, 10:41 PM   #6
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Dust alert can give a false positive if there is any object/shadow in the image. I've found that even a cornice or wall edge can create artefacts.

Whatever you use as a blank light coloured surface (not a lens cap!!!) - it must be a completely blank untextured surface. One of the camera store techs I know uses his computer monitor with a pure white background only visible (he has a file for the purpose) - making sure that none of the screen edges are visible.

Cheers
08-25-2010, 10:45 PM   #7
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QuoteOriginally posted by MoiVous Quote
Dust alert can give a false positive if there is any object/shadow in the image. I've found that even a cornice or wall edge can create artefacts.

Whatever you use as a blank light coloured surface (not a lens cap!!!) - it must be a completely blank untextured surface. One of the camera store techs I know uses his computer monitor with a pure white background only visible (he has a file for the purpose) - making sure that none of the screen edges are visible.

Cheers
+1, exactly.
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