Hi everyone, I am just beginning to start astrophotography. Recently I tested out my equipment and I have a couple of questions.
Firstly, I use a Nikon D90, Skywatcher 130 PDS and an EQM 35 pro mount as my setup.
I decided to point my telescope at the Double Cluster last night just to see if everything was working properly.
I took 50 or so 10 second subs at ISO 800. However, upon examining the photos I noticed there are cross shaped stars in the image, mainly towards the fringes. I have attached a close up of the bottom right part of one 10 second sub. Is this an issue with tracking or vibrations, or perhaps an issue with collimation?
Another question: when I tried processing the image in GIMP, I noticed a discernible darker ring around the fringes of the stacked image. Is this coma and should I invest in a coma corrector or can I correct in GIMP?
Thanks everybody for your help!