Re: Curious Artifact in Images


Gregg Ruppel
 

Steve
Those are really WEIRD!  I have never seen any thing like them, but from the size it would seem that they are far upstream from the sensor (compared to some of the dust donuts).  They look like diffraction rings from far out of focus stars.  My guess would be that there is some small but very reflective object(s) in the OTA that are catching light from a star, not necessarily a bright one.  Good luck tracking this one down.

Gregg

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On Jan 27, 2019, at 11:56 AM, 'Steven Reilly' sreilly24590@... [ap-gto] <ap-gto@...> wrote:

 

So I started imaging NGC2359 back in 2016 and have acquired some data every year since but one thing that plagues the images is an artifact that really is something I don’t seem to be able to track down it’s source. I’m not sure if it’s a defect in the flattener, a reflection in the ota, or something in the imaging train. My suspicions are with the flattener but I don’t know how to qualify that. For the record it isn’t an AP flattener and this is using my OGS 12.5” RC with the STL-11002M with optional filter wheel. This type of artifact randomly seems to appear in various images. Let me qualify that, it may appear in some images of the same object regardless of filter used while in other images there are no traces whatsoever and everything looks normal. Of the images I’ve seen this is LBN999, where there seems to be 3 sets of these arcs while in NGC2359 there is only one and they are in different locations. With Thor’s Helmet I choose a different guide star moving from a PA of 154 to 323 and saw the artifact keep basically the same orientation to the nebula rotated almost 180 degrees. The LBN999 image appears to have 3 sets of these in a triangle in the lower left corner of the image. Image Linking these in TheSkyX shows no extremely bright light sources close to the FOVi.

 

Any suggestions on how to try and find the source of these artifacts and a possible cure? The one way I think this can be resolved is to remove the flattener and live with the less than round stars in the outer boarders of the images but that would be the last resort I would hope. In order to remove this and add spacers to properly distance the sensor would be a good deal of work, doable but not that easily. And then of course I’d need a clear night to test.

 

Thanks for any suggestions. The images in question can be found here. Actually there are 3 web pages created at different times and they are linked together here.

 

-Steve

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