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RASA8 and ASI2600MC star issues

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Just received my 2600MC to go with my RASA 8, first light was last night and the first couple images (between clouds) produced some promising results. On closer inspection it looks like i may have tilt/backspace/focus issues, one corner has donuts(bottom left), and star trailing top left and right, and bottom right.

I ran the stacked image through CCDI and got the following 2 results. 

So my question is, is this just a tilt issue, will fixing the tilt also fix the curvature, or at least reign it in a bit. I am using a starizona filter holder (with the 5mm spacer) and the RAS8 clear glass removed. I am also using a ZWO EAF for auto-focusing


I am not looking for perfect stars, but the only donuts i like are in ma belly :)


Any help/advice is appreciated.








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I don't know if this will help but i have seen online somewhere what to expect when you have spacing issues from what i can remember if it is too much the stars will look as if they are trailing one way & if it is not enough the trail will be the other way.

Also i read that you had to make allowances for the thickness of the filter, so if the spacing for your camera is 55mm you have to add another 1mm for the filter.

Hope this helps

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Needless to say at f2 and a large sensor the RASA8/2600 combination is super sensitive to both spacing and tilt.

Folks have made low cost test rigs to measure tilt off the telescope, which may be of interest:


Edited by tomato
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4 hours ago, tomato said:

Well, at least it’s not as subjective as other aspects of image processing, stars should be small and round, right? 
You’ll notice I didn’t mention colour.

I know, but making them round in software seems a bit like cheating :D


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  • 3 weeks later...

I've had issues with tilt as well with my RASA 8, which was caused by the adapter not being centered perfectly in the retaining ring. I've read many forum posts that attributed the issue to collimation, spacing etc. Didn't matter if I were using the Starizona Filter Drawer or Artesky holder, I wasn't getting flat images (I even started some nights centered only to have the adapter slide around and cause the tilt). I've ordered one of these from a printing service and I've been getting a flat field / nice stars in the corners ever since: Thingiverse

May not be the cause of your issue, but maybe something to consider before messing with collimation or pulling your hair out messing with the spacing


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