Even at apparent clear night skies there can be a lot of stray light that becomes visible at longer exposure times in astrophotography. By means of software the stray light can be reduced, but at the same time object detail is getting lost in the images. The following picture of the area around the Pinwheel Galaxy (Messier 101) with the apparent magnitude of 7.5m with all stars down to an apparent magnitude of 10m was taken in Berlin in direction close to the zenith with a fast lens (f-number 1.2) and an exposure time of five seconds at an exposure index of ISO 12800: