Weird output from DSS

[TractionMan]

Last friday I decided to give the iOptron SkyTracker V2 a proper run and try to image M31 with the zoom lens (Tamron 70-200) set to 135mm. However, the clouds magically appeared before I got the chance to tweak composition and polar alignment. Only got a few 45 sec subs but decided to play with them in DSS anyway. 4 subs and 3 darks stacked, but the result looks really weird. I got some very odd streaks and artefacts or whatever it is. Anyone who can tell me what it is or how I can avoid it?

I didn't bother to try to do any more processing to this image, just brightened it up a bit to show you the strange artefacts.

[Thalestris24]

Hi

Not sure - probably not to do with dss. Maybe dew? Possibly a reflection. What are individual subs like?

Louise

[Uranium235]

If almost looks like hair (!) on the sensor to me. Take some flats, that will confirm it.

[TractionMan]

Hi

Not sure - probably not to do with dss. Maybe dew? Possibly a reflection. What are individual subs like?

Louise

I can rule out dew since I checked it every now and then while taking the images (the lens hood made a good job there  ). Reflections, perhaps, but I doubt it. The camera was properly obscured from any light source. Going to check the subs when I get home from work.

If almost looks like hair (!) on the sensor to me. Take some flats, that will confirm it.

Hmmm it didn't occur to me that it could be something like hair on the sensor since I'm usually quite pedantic with keeping the sensor clean. However I just got the DSLR back from service (got the motherboard replaced) and I didn't clean/check the sensor upon arrival. Will do that as soon as I get my hands on it again.

[TractionMan]

Finally got time to check the sensor and individual subs. The sensor was clean, not even a tiny dust bunny to be seen. Next I checked the subs by brightening them up with ACR. Not a trace of the weird artefacts/streaks on any of them. Very, very strange. Just to be sure, I checked the dark frames as well with the same result, no artefacts there either.