[Startrek (Martin)]

I’ve been successfully imaging with my little 6” f6 Bintel GSO newt for nearly 5 years now and the last 2 nights ( which have been pristine conditions in Sydney ) I’ve been trying to resolve wonky stars (Star shape is a mixture between trefoil and rectangular , not really bad but noticeable across the field , all stars big and small are affected ) Sorry no images
I’ve had coma in all my newts so I know the signs , this is not coma or tilt
Achieved good focus as Ive done a thousand times before using a mag 2 star ( Alnair ) focus star is zoomed in 5x with diffraction spikes like sharp swords and centroid nice and round. Nice tight Focus Star
Both nights pristine conditions and my PHD2 Multistar guiding has been 0.50 arc sec total rms ( Dec and Ra even stevens )
My PA is around an arc min. Took an 80 sec exposure on my focus Star Alnair and zoomed in 5x . Alnair still had good shape , no eggy or odd shape
Using a Baader MPCC coma corrector like I’ve used a thousand times before
Tried some 0.5mm Shims , added one then two. Star shape still wonky so went back to my normal spacing

Remove mirrors and clean
Check primary mirror rubber clamps for possible pinched optics, they were nice and loose but not too loose
Collimate scope using laser and Cheshire like I’ve done a thousand times before. I always check to see if focus tube is clear of collimated view
Collimation spot on
Took a 90 sec image with camera way out of focus. You could see the collimated view of the scope in each of the stars. Then re focused nice and tight
Goto, focus , framing , guiding , capture all working fine as it’s done a thousand times before
EAF focuser working ok
Tried moving the primary mirror forward by 3 to 4 mm using some fibre washers but that just introduced more vignetting, so put the primary mirror back to its normal position
Checked focuser for slop, couldn’t feel any noticeable movement laterally, Focuser is pretty solid
Tried imaging with and without my L Extreme filter , no difference still wonky stars
Checked camera front plate for tilt with feeler gauges , same thickness all the way around as always, hasn’t moved
Insert camera into focuser with care to ensure it is flush and square as I’ve done a thousand times before
Used M83 and NGC5128 as test objects
Took 90 sec , 120 sec , 180 sec and 300 sec exposures on both , still wonky stars on all images
Also tried different gain settings on camera , stars still wonky

What has got me stumped I was imaging NGC 5128 3 nights earlier under crappy conditions ( heavy dew ) captured 50 x 90 sec subs , guiding was around 1.00 to 1.50 arc sec and stars were round , bloated due to seeing but at least round

3 nights later , same set up , same procedures and stars look crap , sort of blocky or triangular shaped ( not bad but noticeable)

Also another thing that’s got me stumped is that my focus Star looks perfect zoomed in 5x

But looking at a complete sub in APT plus using Astap , stars are crap across the field

Sorry for the long winded explanations but I’ve run out of puff trying to resolve the issue

It’s has to be Optics or in optical train but I’ve run out of ideas

Maybe the primary mirror is stuffed ?? It looked visually ok after I cleaned it

Comments, ideas , suggestions all welcome

Thanks