I just recently received my Canon EOS T3i back from having had the full-spectrum mod performed (i.e. stock filters removed and clear filter installed), and put this on my William Optics Zenithstar
61II for some test frames under Orion last Wednesday. What I'm seeing in both the 5 second and 60 second exposures, however, seems to indicate I may have some filter issues resulting in star bloat.
I'm using in Astronomik L-2 UV-IR APS-C clip-in filter, and also have a 2 in Optolong L-Pro installed in a field flattener for light pollution (Bortle 5 where I'm at).
I understand the refractor is an APO Doublet, and the conditions weren't completely ideal (moon was 46%), and I also have a sturdier tripod on order to better support the Skywatcher Star Adventurer 2i and optics... but it still seems like things aren't quite right. I used the Bahtinov mask for focus before imaging and I got an X pattern, and am reasonably certain that it wasn't knocked out of focus when I went to Orion.
Do I need a more aggressive UV-IR filter like the Astronomik L-3? Is this more likely a focus issue?
I will also mention that the night before I shot the same target with a full-frame mirrorless, non-modified camera (so I didn't use the Astronomik L-2, but otherwise had the same setup) and did not see the bloated stars.
I'm a beginner, and an aspiring astrophotographer, so I could be missing something due to lack of experience. Any tips or suggestions are welcome
The attached thumbnails are unedited (I shot in RAW, but these were exported thumbnails):
Exposure: 5 s on one, 60 s on the other
Here's a link to the full RAW files for these two: https://adobe.ly/3c1Xc26