ED80T, CEM 40, EOS 80D, (50MM guidescope + ZWO ASI), Field Flattener
I took 30x 150s ISO 1600 lights and dark subs of M31 last night + 50 bias.
Near full moon, but otherwise clear, temps around 30-32C (per CCD image)
Stacked in DSS, 90% best frames. Quick curve stretch in PI.
Here's what I'm seeing that confuses me:
1) The noise on the left edge of the image is substantially less than everywhere else.
2) Stars on left side are also elongated - but nice and circular everywhere else - and tracking (PHD2) was good all night long
3) Strangely perfectly circular dust spot on upper left.
Any ideas what's causing this?
I looked at stretched versions of the dark and bias masters. Dark looks like random noise, bias looks mostly flat, but you can see some vertical banding.
I didn't take any flats - but is this kind of difference in noise across an image normal w/out flats?
Edited by ParagPA, 11 September 2019 - 03:05 PM.