what is this.......

My C80ED does not show a complete diffraction ring around brighter stars than, say, mag 2-3.
Instead I see an half arc of diffraction ring at 160X. On the other side of the star there is no diffraction ring at all.
Out of focus I see very nice concentric an even rings, almost identical on both sides indicating no flaws at all. Maybe a bit washed out outside focus compared to inside.
I split 1.5" binaries and split delta Cyg on good nights, observed Io and Europa transits as well as GRS last spring altough Jupiter was low in the sky, observe craterlets in Plato, Cassdiv and Crepè ring as well as subtle bandings on Saturn, lot of markings on Mars last apperation as well as SPC. So there is not much wrong with the scope. But the "half diffraction ring" around brighter stars is ugly and irritates me.
So what is it....misscollimation? Too bad in that case as C80ED can`t be collimated as far as I know
Has anyone else the same experience?

Clear Skies,
Magnus

PS I use WO 2" diagonal Intes 2,2X Barlow and 9mm Antares eyp.
The same equipment with my 120ST shows a very nice diffraction ring at focus on brighter stars at 160X

Magnus, Can the focuser be collimated at all? It sounds like a slight misalignment problem to me.

>>So what is it....misscollimation? Too bad in that case as C80ED can`t be collimated as far as I know >>

It is a slight amount of miscollimation, but no amount of tilting of a lens cell would fix this. The problem is that the three spacers are not quite exactly the same thickness. The way to get it perfect would take a long time for a properly trained technician to do, and that would have cost more in labor costs than you would have wanted to pay.

Rolando