I'm experiencing some difficulty with amp glow not calibrating out and I want to get a better idea of what I'm doing wrong.
I am operating from the working hypothesis that it's because I am over-stretching my images, but I'd like to get a bit of wisdom from others here who may have defeated this particular monster.
My gear is entry-level mono: QHY183M with William Optics Zenith Star 6.1 (=focal length 360mm, f/5.9)
Mount and guiding etc are unimportant to this conversation. I can get perfectly round stars at all exposure lengths I've tried (up to 360sec) and I've no cause to doubt I could easily push that to 600
Filters are Optolong 1.25" - the 6.5nm ones (Ha, SII and OIII)
Rounding it off is a Pegasus FocusCube2.
Attached is a processed Ha stack.
Subs are 300Sec at gain 20 (unity on this cam is 10, valid range = 10 to 54) with the sensor at -20ºC and an offset (bias) of 40
This is a stack of 20 subs
Darks are the same settings as the lights, just with the lens cover on
Bias frames are same temp and offset and gain, min exposure (0.0005sec)
Flats are the same as well, using an iPad screen with camera at zenith, usually around 1sec
No dark flats
USB Readout speed is 0 (zero) for all - lights, darks, flats, bias.
Stacking - I'm using DSS at its recommended settings, ensuring "dark frame optimization" is not checked.
Still with me? Cool. So if you take a look at the jpg you can clearly see the amp glow hasn't fully calibrated out. And worse, it's thrown lines across the image as well.
So - my hypothesis (please either validate or correct if wrong) is that I'm not gathering enough light, and consequently having to over-stretch the image, to the point where I've exceeded the ability of DSS to calibrate out the remaining amp glow. And that the fix for this is either or all of:
- Shoot at higher gain, or
- Shoot longer (600s subs?), or
- Use a faster optic
Side note I haven't had this problem shooting LRGB (or maybe it's still there but I am just not seeing it because I don't stretch those so hard)
I can put up a sample FIT file from the camera, and the PSD that generated this jpg, onto a cloud somewhere if anyone wants to download it and have a play.
If anyone has any thoughts I'll welcome it.
Edit\Add: I've put the PSD, and the darks, lights and bias frames on a download link for anyone so inclined to download 1.2GB https://1drv.ms/u/s!...fETy_A?e=Vn93v8
Edited by adamrosner, 25 January 2023 - 03:50 AM.