Just finished stacking frames from a session on the Iris Nebula and I'm noticing that as I get closer to the edges of the image, I am seeing "spikes" coming off my stars in a particular direction. My setup is as follows:
William Optics GT81
Flat 6AIII (.8 reducer)
I attached an example of what I'm seeing. I'm interested to learn what would cause these spikes. I'm assuming it's a focusing issue, or is it just inherent with the type of scope I have, flattener and size of my camera sensor. Could it be that my backfocus is off? I do use the Bhatinov Mask that came with the scope to focus and feel I'm doing a reasonably good with that. My stars towards the center of the image generally look good.