Circular gradients problems

[originaltrilogy]

I get ring type gradients with QHY8 and tends to green.
Is this just because of moon making light pollution ar am I doing something wrong?

[A23649]

Are you taking Flats?

[Shiraz]

Green is due to light pollution and airglow - I get the same with my QHY8. Rings looks like an interference effect. A few things that you might look at - clutching at straws a bit though:
- does it occur if you take a flat field image through the optics?
- was the QHY8 dried out properly before use - maybe a film of condensation or ice somewhere?
- Did you have moonlight falling directly onto the front surface of the lens?
- what filters did you have in the system?
- was the sky very hazy, or with thin high cloud?
- Is it possible that any optical components have a thin film of fingerprint grease or oil on them?
- is this a new effect (has the system worked OK before this)

[originaltrilogy]

Moon was nearly full and high in sky. I will try when no moon and see if still green.

I used very long dewshield to keep moonlight of lens, but is very fast scope. Maybe my subs are too long or short?

Only the IR filter in the nosepiece of QHY8, is colour model.

Sky looked very clear and not many twinkles of stars, optics very clean.

I need to collimate lens system though, this is first light attempt to get to know how to make camera work with softwares.

[Poita]

I think your main problem is just trying to go for faint galaxies during a full moon!

I had a 30 second go in photoshop just with curves and levels and still managed to extract this, so you are getting plenty of data.

Clean that chip, take flats and get out when the moon is gone and I think you will get some impressive images.
If you have to choose between getting good flats or darks with the QHY8, go for the flats, the darks are less important on that camera IMHO.

[whzzz28]

This is most likely your problem.
Moon/skyglow won't cause a spherical gradient. Instead you will get a gradient affect to one side (whichever the moon is on).

Did a quick and dirty combine of some subs taken from my back yard. Not flats applied or post processing done (apart from histogram transformation to show the affect).

You can see the spherical glow, and to the top right is a green gradient from the corner. The green is sky glow from Brisbane city and the spherical glow is normal as this has no flats applied.

Apply a flats to the subs and the spherical glow disappears, you can then use a gradient removal to remove the green sky glow.

PS: Full moon doesn't help, but you will still get images they will be washed out a bit though and won't look as good as if they were taken during a new moon. If it is a full moon i generally tend to image something that is on the completely opposite side to which the moon is so i don't get reflections.