Strange shadows-wrong flats? Humid in filter or sensor problems?

[mislav]

I tried last night orion... 90subs 20sec 800iso with nex5n full spectrum and vivitar 135mm f2.8... after about 20darks and 20flats (blank copmuter screen 1/10 exposure .. i was cleaning sensor few weeks ago and i usualy get nice pictures..without this quadrangular strange shadow ..whats the problem???

 

[Thalestris24]

Hi

Not sure what you mean but it could be a processing artefact or light pollution.  What are individual subs like? What have you used to stack and process the image? It looks like you have some field rotation or possibly tilt - worse in bottom and bottom left. What mount do you have and how did you do PA? Also, I think you've maybe shifted the image a bit too much towards the red. You should probably take bias frames and dark flats rather than darks.

Louise

[mislav]

dark flats? i know dark, a know flats, but dont know dark flats:)... mount was photographic simple mount, with nanotracker... DDS stacking 90% best images kapalambda..light polution could be...i am in centre of capital city..Red engancer with full spectrum isnt such a good idea-very hard to play with colors and red..

[Thalestris24]

5 minutes ago, mislav said:

dark flats? i know dark, a know flats, but dont know dark flats:)... mount was photographic simple mount, with nanotracker... DDS stacking 90% best images kapalambda..light polution could be...i am in centre of capital city..Red engancer with full spectrum isnt such a good idea-very hard to play with colors and red..

Dark flats are darks with the same exposure as your flats. What software did you use to process the image? Did you align the histogram peaks in levels? The nano tracker looks difficult to polar align. A 135mm lens is maybe too long for it. Try it with a standard 50-55mm lens.

Louise