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A great first image.
Dust donuts are removed by flats and are typically on the filters or the sensor window.
Its a good practice to keep them clean and not rely totally on flats to get rid of them.
An easy way to do flats is a white tshirt over the end of the scope, point towards the NW at dusk and take 3-5 images with each filter
and aim for an adu level of around 20,000. Then take darks for the same length exposure and do median combine in CCDstack and dark subtract them to create a master flat.
Now you have a master flat for each filter.
If you are lazy you can just take one for luminance and use one of the coloured filters only. You can often get away with that unless one of the other coloured filters is really dirty.
Greg.
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