Old 12-06-2018, 10:49 PM
Tony_ (Tony)
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Black spots - dead pixels?


Recently I've notice several black spots on my images - like the group of 5 in this image. Are these dead pixels? If they are why would I get several all at the same time?
I've looked at the sensor and I can't see anything on it, also I've tried cleaning it.

Any ideas what the black dots are?
Camera = cooled modded canon 60d.

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Old 12-06-2018, 11:27 PM
glend (Glen)
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Those are too big for pixels, probably dirt on your optics or the sensor. Check all the camera glass and use a puffer on the sensor to see if you can get rid of it. Shoot a flat to confirm it's there, it should show up.
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Old 13-06-2018, 09:38 AM
markas (Mark)
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You need to determine whether the spots are always in the same places. The easiest way to do this is to use any old lens on the camera and shoot a clear daytime sky, then examine the raw image at 100%. You should see the offending spots easily

They certainly look too big to be dead pixels - but they also look too small and distinct to be dirt on the telescope optics.

If they are always in the same place, it would suggest 'intractable' dirt on the camera optics very close to the sensor. Such spots would be very hard to see directly without careful lighting and some magnification.

I have seen a Canon camera with grease spots on the cover plate which was VERY hard to remove, and required special solutions and tools - not for the inexperienced or faint-hearted! (This example took me several hours of work to remove the offending muck).

If you can establish that the spots are fixed, and not movable by blower, you would need to take the camera to a specialist cleaner. If they are movable, the best way to deal with them is to remove them using a special brush - NOT any old brush!!!. (I use the Visible Dust product range. Have a look at their website.)

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Old 13-06-2018, 09:55 AM
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Atmos (Colin)
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If you’ve processed this image and some noise reduction, that would explain why they’re larger than single pixels as noise reduction will make a single back pixel larger at times.

We’re the frames dithered? If it is a dead/cold pixel then it’ll be removed during pixel rejection if they’re dithered.
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