Strange diffraction spikes

[hjw]

Hi,

I recently took possession of a Saxon 200DS (a Synta twin of the SW 200PDS) and I am struggling to get good images with it. I have a GSO coma corrector and a set of extension rings for it. In general I have trouble to get the star size below FWHM=6 (on the SW 80ED I can get 3.5). On the image the diffraction spikes appear only on one side and it would be fair to call them diffraction "halos". I've tried a few nights now with different objects but seem to get nowhere

It's 15 light frames 180sec, ISO 400. Saxon 200DS, HEQ5, GSO coma corrector, Pentax K-30, SW ST80 guide scope, ZWO ASI120C guide camera

Any advise welcome!

Clear skies!

HJ

[Mr niall]

Is the mirror clean and not pinched in the housing? Have you tried undoing everything and recollimating from scratch? Do you get halos with visual as well?

or maybe try shorter exposures? Could be the stars are blowing out?

on another note - they do look very pretty...