Dark rings

[JemC]

Good evening, 

just out in the garden trying to grab some M51

1st image in and it has some dark rings showing in the image, screen shot below, are these anything to do with dust on the sensor or is it something else, any ideas ?? 
 

[The Lazy Astronomer]

Dust for sure. They should be completely corrected out with flats.

As for the location of the particles, FLO have just released a tool for working that out: https://astronomy.tools/calculators/dust_reflection_calculator

 

[Jonny_H]

Agreed. Dust bunnies for sure.

As the LA has mentioned these can be removed with calibration frames, i.e. flats.