Help - can someone spot what's going on here please?

[SouthEastViewer]

Hi

Am new to astrophotography and have begun using a Nikon D5600 and WilliamOptics Z73 based rig. I seem to be constantly getting circular gradients that interfere with any tone stretching leaving circular bands of colour.

Example attached below from few nights ago.

Does anyone know what could be causing this and how to eradicate it please?

All help greatly appreciated. Thanks!

 

Some data on below:

- 2 hours of light, at 5 mins per shot

- 20 darks, 20 bias, and 20 flats

- telescope is in a place where neighbours flood light has some cast, but is pointing away

- bortle class 5 area

[TerryMcK]

Hi and welcome to the forum. Are you using any light pollution filtering?

[SouthEastViewer]

Hi

Thank you!

Yes, I've the following installed: Svbony CLS filter 

I threaded it into the William Optics Field Flattener.

Thanks!

[GazAstro]

It's difficult to say but it does look like possibly 2 sources of Lp, maybe Moon on one side and street lights etc from the other.

Can you post an unstretched image ?

[SouthEastViewer]

Hi

It seems what I was doing wrong was not properly taking flats. The histogram of my flats was either over or under exposed. When I reduced exposure on the D5600 down to 2 seconds I got a peak in the histogram around 3rd to middle. I redid the biases and on the night took darks too. The results were significantly better.

Also, I moved the scope away from neighbour flood light haze. Not sure if that helped much, but every little helps. 

Here's two consecutive nights worth of Fireworks Galaxy to see if I got rid of excess gradient and noise.

 

[TerryMcK]

Looking much better.