Good Evening All,
I have a William Optics Zenithstar 61 with a 0.8x 61R flattener-reducer, imaging with a ZWO ASI 1600MM-Pro and EFW. I have been experimenting and researching as much as I can and I still cannot figure out why I am getting elongated stars in the corners of my image. I have tried starting at the recommended 56mm of backfocus and imaging in and out from that - yet still the stars are elongated, radiating from the centre as if the sensor and flattener are too close. Below I have attached images from 55-60mm of backspace along with corresponding CCD Inspector maps in the reply (not sure if that's useful or not).
Current theories are optical pinching (it was -10C when these were taken), collimation or I just don't know what I'm doing.
Any help would be greatly appreciated!
Edited by bluewater, 03 February 2021 - 11:29 PM.