New scope setup, unexpected issue in star elongation - would appreciate any advice

geeklee · March 21, 2020

Hi everyone - I recently took the plunge on a new triplet scope and expected it to be a bit of plug and play in my existing setup (both refractors, very close aperture and focal length etc).

I've had the new scope for a month but have only finally got out to test it the other evening. Now I've checked some subs - not much as the cloud cover beat me even in the short time I was out - I can see elongated stars in the top left, bottom, right and to a lesser degree the top left.

Setup previously (510mm FL with 0.85x FR, 1.52 "PP image scale):

ZWO ASI 533 -> 11mm -> 21mm -> 16.5mm -> 0.85x FF/FR -> FLO 2" adapter -> 2" UV/IR cut filter -> Baader click-lock -> 80ED -> focuser untouched

New setup (560mm FL with 1x FF, 1.39 "PP image scale):

ZWO ASI 533 -> 11mm -> 21mm -> 16.5mm -> 1x FF with built-in 2" nose piece adapter (like above) -> 2" UV/IR cut filter -> twist lock on new scope -> focuser rotated 90degrees.

The sensor is really small on the 533 (11.3mm x 11.3mm) but I have the 1x flattener to "tick the boxes" and make sure there would never be a problem...

I'm posting this up as it's not looking good cloud wise for the next week (at least) so I want to make sure I have a troubleshooting plan for when I get outside next. I'm hoping it's something simple and my inexperience is the cause. The new scope was bench tested before being sent so I'm certain the issue lies with something else in my setup!

Things I've done so far:

Double checked the above setup is tightened up. So each spacing adapter and the twist lock on the scope. It's all really solid and I feel no slack or anything similar in the focuser.

Things I think I'll need to do to get more information:

Take a new image, rotate camera 180 degrees, take another image. Compare.
Take a new image, rotate focuser 90/180 degrees, take another image. Compare.
Take off the 1x FF and test the same above.
Put on the 0.8x FF/FR and test the same above.

Here are the image crops and FHWM/Eccentricity output from PixInsight. Two notes:

The focus on the "bad" subs isn't great. One other new addition when changing scope was an electronic focuser and in the rush to beat the clouds (with unending WiFi problems) I was a bit too casual with what I thought was OK. I don't think this is (all) focus related as the rest of the image looks bloated but OK.
The framing is slightly different in each image. They were separate nights without plate solving the previous nights image - again, rushing to test 🙄

"Good" (previous setup)