[AZ-Observing] Re: Water spots?
- From: "Tom Polakis" <tpolakis@xxxxxxx>
- To: <az-observing@xxxxxxxxxxxxx>
- Date: Fri, 25 Jan 2019 14:33:18 -0700
Mike McDonald wrote:
But why did the dust show up when it did? There weren’t any dust spots in the
earlier images that night. I hadn’t disconnected the camera and filters from
the
scope, so no new dust should have been able to get into the system when it
did.
(Unless the backside fo the ZWO camera is open to the fan or something.)
I bet it's on all of your images. Adjust the levels such that the background
is light gray, and you will see the same dust motes on all of the images.
And how do I get rid of the dust? I know, nearly impossible in Arizona! Guess
I
need to check the RGB images to see if it’s on the camera or one of the
filters.
As Paul mentioned, the answer is flat fields. You should take at least a dozen
flats for each filter, and median-combine them. Since new dust inevitably gets
to the sensor and filters, you'll need to refresh the flats periodically. I
showed this comparison in my recent photometry presentation to demonstrate the
magic of calibrating images.
https://i.imgur.com/k0p275p.gif
Tom
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