Although the weather was crystal-clear for the whole night, it closed completely today from about 0.30 o' clock. After all, the first 19 luminances of Sh2-187 were brought in. At the beginning I tried M 74 as an intermediate object. But because the galaxy is very low, I got very conspicuous tubus reflections, which could not be completely erased even by flats. That's how I left it after an hour and returned to my main object in the direction of Zenith.

This is a stack of the 5 raw images of 600 sec. each, which I made from M74 with the CLS filter. The bright ring is clearly visible. I don't know how to get rid of it yet, the flats don't help. Always with low objects I have such scattered light reflections in the picture.

Tommy Nawratil gave me the tip to try an artificial flat and pixelmath. For this purpose I created a flat in Photoshop, in which I first removed the stars and then softened all structures with "dust & scratches" until only the brightness values were visible.

The following formula was then used in Pixelmath: Luminance-Flat+med(Flat). I was really surprised by the result. All gradients completely gone! Super!

The other good news of the night: the first 19 luminances of Sh2-187 look very good: