circle gradients driving me potty!!

[Daniel-K]

ive had a quick go at processing the full image but the circle gradients have come back to haunt me again, no on a single sub but there after its been stacked. looks like my flats havent worked either so i will have to have another go at them. any advice would be great

cannon 450d

subs 155 secs

iso 800

no moon

seeing conditions very good

darks+flats applied

thanks

[Tim]

Cover up the back of your scope when imaging, light going through the back of the mirror will do this.

You'll have to fluff this one but next time you'll know

[Daniel-K]

ooo Tim your a star thank you. but wouldnt it be on the subs?

[Tim]

You'd struggle to see it on individual ones unless you really stretch them, but they get added together in stacking somehow and show up wholesale. Try stacking using "minimum" and see if you still get it. It might even be there in your flats or darks or bias, so stack without them too.

At least, that looks a lot like what I had on mine with an open back newt. I use a piece of corex with black felt on cut to size to cover mine up, otherwise light reflected from the floor enters the back of the mirror. Eve if it isn't that on your image, cover it up anyway.

Funnily enough, the first time I found this on an image was also one of M81 & M82!

You'll get it sorted.

[Tim]

PS Your collimation is out

[Daniel-K]

it ownt be tomorrow when my cats eye combo turns up