Egg Shaped Stars

[ChrisBAgile]

I'm brand new to the forum and new to Astro. I've been loving it since January and learnt a huge amount by myself with the help of forums like these.

I recently purchased an iOptron 10" RC truss. 3" focuser with a 2" compression. I have been using a WO FLT 132 before this which is little more forgiving. I have attached a couple of pictures from my first attempts. I am not using a field flattener at this point. (just getting used to collimating and setting up). Camera ZWO ASI 6200 MC cooled camera. The images below are composed of 50 x 5 minute subs stacked in pixinsight with basic image processing. I'm using PHD II and a WO guidestar 61 and ASI 120 for guiding on a CEM60EC mount. Drift alignment in PHD 2. Any ideas as to the main causes of egg shaped stars? Could this be sensor tilt? crappy guiding? Focus also looks off? Any help appreciated please

 

[RolandKol]

Never had this scope...

But my SW 130PDS had exactly the same egg shaped stars/coma while imaging without a coma corrector...

However, your scope manufacturer states it should be coma free...

Not sure, and do not know  what collimation steps your already done, - maybe it could cause it, but I doubt it would for F8 system.

Edited May 18, 2020 by RolandKol

[ChrisBAgile]

Thanks for the reply. I'm collimating with a Howie Glatter Laser Collimator and confirming with star test. I'm new to collimation though  

[happy-kat]

First thing is check your laser, if it needs collimation you need to fix that first

[michael8554]

I think the problem is most obvious on the second image, all stars elongated in the direction TL to BR.

But you have shown stacked images, we should really be looking at a single sub, stretched if necessary, to eliminate any stacking effects.

And ideally a 10 to 30 sec sub, to eliminate guiding and tracking errors.

Michael

[ChrisBAgile]

Here's a single sub stretched. It's clear tonight so will also look at getting some 30 sec subs.

[michael8554]

But of a puzzle, as I'd say Coma-like distortion TL, BL, BR, but Top Right looks okay.

Lovely smooth exposure compared to my DSLR !

Michael