ZS 61 II – pinched optics?

[Neil Heslop]

Good evening,

Need an opinion on some imaging from a small refractor set up please. My first scope. Purchased new about 3 months ago.

I have placed some files in a Dropbox here:
https://www.dropbox.com/sh/lqtqvwav9rczdvn/AABaba29E10Gx2BFDFgSx1gja?dl=0

The larger/brighter stars all seem to have small lobes attached to them that you can see from the FITS files – mostly visible on the bottom left side of each star but also a little on the bottom right. Stacking with calibration files (darks, bias, flats) didn’t help. The effects are across the field not just on the edges.

Pinched optics? Scope out of collimation?

My setup is as follows:
Z61 II with Flat61A adjustable field flattener on an iOptron CEM26
Optolong L-enhance 2″ filter mounted in field flattener
Imaging Camera ZWO ASI 533 MC
Guide camera ZWO 120 Mini MM
Guide scope ZWO 30mm f/4 Mini Guide Scope.
Properly aligned using iPolar and guided with an ASI AIR Plus system. Guide errors were very small and within the limits of the image scale.

Imaging taken in a Chch backyard with ambient temperature around 5 degrees C.

Focused easily enough using bahtinov mask which was quite reliable, then locked and slewed to target. Not refocused during the sessions. Any advice appreciated please.

I’ve run 2-3 sessions since. Same result, different targets. Suspect it’s been a problem since new.

TIA

[Author]

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