[Pierre_C]

Hi people.

I am new to astrophotography and have just started using a DSLR on a tracking mount for the first time.

Can you tell me what is going on with the bright blue gradient across this picture? I was expecting it to be all the same background colour.

This issue became apparent when I adjusted the photo by turning the brightness setting down from 50 to 0 to bring out the starry detail.

I used a Nikon D7000 DSLR with a Nikon Nikkor 18-105 zoom lens on a Sky-Watcher EQ3 mount with RA drive. The lens was set for a nightscape at 18mm and the exposure was 10 seconds at ISO 1600.

We are looking south along the meridian.

There is some Milky Way running vertically through the centre of the photo (Crux with the Emu Head are just below centre, and eta and theta Carinae are above centre) but the bright bit to the right seems excessive. The top right corner is also very dark, which seems odd.

The city is 25km to the west – to the right of the photo. The picture was taken after astronomical twilight. There was no moon. I did not notice any clouds.

Could it be due to something to do with the zoom lens or the camera sensor? Or something else?

Thanks.