I'm having quite the conundrum trying to figure out why my stars are looking like balls, rather than ... well, stars.
I shot M31 over two nights, first night doing 60s exposures, second night doing 120s exposures.
Both nights I shot Bias, Darks & Flats separately for each, making sure to adhere to best practices around camera temp, position, etc.
- Scope: Askar FRA400 + f/3.9 Reducer
- Focuser: ZWO EAF (star ratings were around 3.1 for both nights)
- OAG: ZWO + ZWO 120MM Mini
- Filter: Baader Neodymium IR-Cut
- Camera: ZWO 183MC Pro (Gain 120, Temp -10°C)
- Mount: AZ-GTi (RMS ~1.5" for both nights)
- Control: ASIAir Pro
Integration over two nights:
- Lights: 70x 60s + 50x 120s
- Darks: 60x 60s + 30x 120s
- Flats: 30x + 30x
- Bias: 60x + 60x
I'm thinking it could be:
- the filter (though someone on IG with the same filter got perfectly fine stars using it),
- focus (it looked pretty well focused to me?)
- some form of high altitude clouds / bad seeing (but what are the odds that would be the case on both nights?),
- backfocus (although I did do the math properly, so I'm not so sure on this one)
- some combination of the above / something I don't even know about?
Used APP and its Multi-Session feature to combine the two nights' integration here:
1:1 Size, Stacked:
Here's the same as above, but at 1:1 pixel size so you can properly diagnose the issue.
1:1 Size, Single Sub:
Single sub, stretched in Siril to reference against the stacked and calibrated from above.
Even in this single sub, it's weird that I can see tiny, about 9 pixel sized, stars clearly in focus and being more than a single pixel I doubt they're hot pixels. Even if they were hot pixels, surely Darks would've just taking those out, anyway. But no, it's a very similar affair to the stacked and calibrated version above.
So, in my best Seinfeld impression, what's the deal with these stars?