Re: Can't get less than 1" total RMS

Henk Aling

On Sat, Jul 24, 2021 at 05:56 PM, Alexander Varakin wrote:

I think your mount is fine.
So there is hope?  This was actually as good as it gets.  No wind, apparently good seeing.  At full moon the Veil is not much to look at but the stars were fine and after I fixed some obvious problems the guiding was pretty good.

I looked at your guiding graph and the 3rd section seems to be pretty decent - 0.7" total RMS. I see that your mount has to correct DEC consistently, which means that you have some PA alignment issues. 
Hmm I did a PA alignment with plate solving, should be good.  However I imbalanced in DEC by pulling the tube down in the rings.  Maybe it was bit too much.  With SLW good balance should be fine so let me balance it again.

I opened your stacked image and ran DynamicPSF and got about 4.5 pixels of FWHF, which is about 2.6" at your image scale.
It is pretty good for regular seeing.
It am getting a similar value for my images.
Nice to know!

Given that this is a very short stack, deconvolution did not work well. 
I noticed that you have a little bit of miscollimation going on - stars on right hand side are round and on left hand side have some coma.
I collimated it while setting up.  I wonder if the mirror moves or maybe the alignment of the camera inside the focuser is off.  I noticed the same as the subs came in, definitely something optical.  I will keep an eye on it.


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