Atik Cameras Forum

Support (Please note, this is primarily a user forum, for direct Atik support, please email support@atik-cameras.com) => 3- and 4-Series Cameras => Topic started by: mickhyde on March 20, 2013, 10:27:41 PM

Title: Dark circles.
Post by: mickhyde on March 20, 2013, 10:27:41 PM

So what causes these dark circles in the left image? Flats removed them OK as you can see, but I'm curious.
I checked the glass window on the camera straight after imaging, and it looked pretty clean.
Dust, condensation??
Atik 460EX, cooled to -10C.

Many thanks.
Mick.

Title: Re: Dark circles.
Post by: joelshort on March 21, 2013, 01:20:41 PM

Those are caused by dust or other things somewhere in the image train.  It could be on a reducer/flatener, filters, or the CCD glass.  The smaller the dark circles the closer the dust is to the CCD.

Title: Re: Dark circles.
Post by: topboxman on March 21, 2013, 04:57:39 PM

Nice job calibrating flats with the lights. It not only removes dust motes but flattens the whole FOV very nicely.

Peter

Title: Re: Dark circles.
Post by: STW HH on March 21, 2013, 05:24:25 PM

Hi Mick, all statements have been done.
 Condensation Looks like cristals and concentrate  not in the middle of the Picture.

By the way, how Long did you expose your flats?

Joe

Title: Re: Dark circles.
Post by: mickhyde on March 21, 2013, 05:51:25 PM

Many thanks all for the comments.

I'm glad its dust in a way, don't want any nasty ice crystals.
Strange thing is I've cleaned the glass with a q-tip couple of times, but the circles never seem to move  :-\
Also as you say, it has flattened the view.

The exposure for the flats was 0.100s, using a laptop screen with white background pressed against the Takahashi scope, with the infamous white t-shirt in the way.
I took a number of exposures and this histogram looked the best. Worked really well  :)
See attached histogram.

Cheers,
Mick.
http://www.flickr.com/photos/mickhyde/
http://astromick.blogspot.co.uk/
Twitter @mickhyde

Title: Re: Dark circles.
Post by: joelshort on March 21, 2013, 06:02:44 PM

Try rotating the camera in the focuser and take another flat.  If the dust circles rotate with the camera, then you know the dust is somewhere on the CCD glass or in the CCD chamber itself.  If the dust circles don't rotate with the camera, then you know the dust is somewhere in the telescope or filters etc.

BTW, you are NEVER going to get rid of all dust circles.  That's what flats are for.

Title: Re: Dark circles.
Post by: mickhyde on March 21, 2013, 07:07:56 PM

Thanks, good shout, I'll try that and let you know.  :D

Cheers,
Mick.