Help requested troubleshooting weird star shapes.

[frugal]

Ok, so I have been playing with the 80ED-DS Pro, on a AZ-EQ6-GT mount, and I have been getting better. I have sorted out the balance issues, and I have sorted out the levelling on the mount. I am not guiding, so I am needing to keep my shots shot (3 minutes is the most I can manage, 2 is more common). However I am still needing to throw a lot of shots as they have strange shapes.

The scope and mount are set up on the patio. The patio is made of solid concrete slabs and there is no movement in them at all. As far as platforms go, it is very stable. I have even made a point of moving back inside to ensure that vibration from me shuffling around is not causing the problem.

I can get the polar alignment down to 1 arc minute, and I perform a PAE correction, by aligning again to a star near the target.

My issue is that about half of the images have the stars appear as dumbells. Strangely enough it is not all of the stars in a batch as I would have expected, it seems to be every other one.

Here are two very close crops (300x200) of a couple of single frames (5200x3500).

About half of the frames come out with nice looking stars like this:

and the other half come out like this (some are more like this, some are just a bit elongated):

Is this just a natural side effect of not guiding?

Is this cone error?

Is this Periodic error and I need to perform PEC training of the mount?

Any help would be greatly appreciated. If it was just an alignment error I would have expected a straight line, but this looks more like it quickly jumped from one stable point to a second stable point.

The final image looked like this, which is a lot better than my previous attempts, but it would have been a lot nicer not to have thrown away half of the data ;(

[Leveye]

Looks like a guiding error to me. It stopped tracking.

[steppenwolf]

Your final image finished off looking very nice. The elongated stars could be caused by periodic error with a particularly poor spot on the worm hence the good'un, bad'un pattern you are getting. This is definitely not cone error. The tracking error is quite severe and apparently 'jerky' so it is just possible that there  is some swarf in the gears.

To be honest, the key to this is auto-guiding. Once you start guiding, imaging becomes so much better and more reliable. The AZ-EQ6-GT mount is a good value mount but it does require guiding for long exposures, it's the nature of the beast.

[frugal]

Yes, I know I need to use guiding to get longer exposures, but I wanted to make sure I was not plastering over a more serious error before hand.

I got the scope and the mount in the FLO clearance sale earlier this year. I managed to smuggle them in as they were a bargain, if I had added a second scope and a guide camera to the order I think I would have been shot I will be looking for a guiding solution at IAS tomorrow I think.