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WO ZS II 80ED aberration

mircea
27 Jan, 2020 16:15
Hello

My William Optics Zenithstar II 80ED refractor seems to have a problem.
While in focus, the brighter stars show a small tail.
While at first I believed that years ago this issue did not exist with the scope, at some thorough examination of older images it seems to be there.
It seems that this problem increases over time, but then again, that might be just in my head.
While in my posession the scope has never been dropped, I've built a padded case for it years ago and treated it like one is supposed to.
When I have noticed this problem I took the objective apart, noticing that there were no alignment marks on the lens edges, so I marked them at that time.
At my latest star test I rotated the front element (the thinner one) and the error rotated accordingly.

At the links below one can see the intra- and extra- focal image, using an artificial star and Antares.

Artificial star test

Altair test

The lenses - and the lens cell also  -do not show any features or defects at all on their surfaces or along their edges.
Could use some help in identifying its possible origin or type.
Could also use some advice seeking - just in case - a lens doublet (ED if possible) to replace the current lens/es
I used Aberrator looking to identify the type of error, but nothing that it can simulate does not come close.
The only thing that might come close, but far from identical, would be the Misalignment error, as can be seen in the screen capture image, but it is quite different from what I manage to see in the videos above.



carastro
27 Jan, 2020 18:56
I see what you mean It's like a 2nd star on the side of the main one. I have had similar problems from time to time and put it down to a nudge on the mount (only showing up in the larger stars).  Is it possible you have a tracking error?

But don't take my word for it I must be the most non technical astrophotographer on Astrobin.

Carole
mircea
27 Jan, 2020 19:48
Well, I've had lots of nudges and I know how they look.
This contraption appears on all frames. Identically.
 
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