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07-23-2011, 06:31 PM   #1
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Dust Alert on K20

I am not sure what to believe. I used the Dust Alert feature on my k20 and it showed this:

I couldn't believe the sensor would be so dirty as I take care when changing lenses, use a rocket blower every few month and do a wet cleaning may be once a year.

So I went out and did what I usually do to check for dust and took a photo of the blue sky with F22. (The wires in the photo are for my orientation, so I would know where the dust is.)

This is what it looks like:

So do I believe my own eyes or the K20 dust alert feature?

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07-23-2011, 08:28 PM   #2
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Hi, Lenp
Your test shot is too dark, I think, to show up dust
Here is what sensor dust looks like

There is actually another dust spot in the trees but not easily visible.
It seems the dust shadows are only easily visible in a range of luminance on the high side
and then they become invisible when the luminance is overexposed.

I have made a "Dust Hutch" for lens changing, cleaning, neg processing etc
It has made a big improvement to dust problems generally.
The above problem was corrected by gently blowing filtered air upwards to the sensor with the camera face down.
07-23-2011, 10:49 PM   #3
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Well, you've discovered one of the problems with the dust alert. Any movement or real texture in whatever you're aiming the camera at will show, as dust. Wombat may be correct, too dark to see the dust but it usually at f22, will show up pretty black.

07-24-2011, 01:20 AM   #4
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Hi lenp,
encountered same thing. Try point your camera at the white ceiling. Think it helps!

07-24-2011, 07:40 AM   #5
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Thanks everyone. After panicking and posting my message, I went to the manual and read how to use the dust alert function correctly. I was not pointing at a white surface when I did it the first time. I just did it again, correctly this time, and the sensor is clean. I also reshot the sky at f22 and did find one small speck (it is visible in the top third of the photo in the middle).

Lesson learned: read the manual... But I am relieved.

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