Flats with dark corner

[toxic]

hi could some one help me please i have had my primary mirror cleaned and put it back and collimated now i am getting flats like this the first has been stretched the second untouched the image train is - atik 383l+ _ efws L filter _ skywatcher cc _ skywatcher 200PDS.

[geordie85]

To me it looks like it could be due to tilt.

[toxic]

thanks Geordie ill have a look at that

[Jannis]

I don't know if it might be relevant, (or if you even still have this problem?) but I had problems collimating my Explorer 200 PDS after cleaning the primary as well. In my case the issue was mainly due to two things:
1. the laser itself was out, after an hour of fine adjustment it was good to go - just to find out that;
2. the scope/mirror/focuser flexed enough to give me an inaccurate collimation using the laser as normal. I could collimate it perfectly, then flip the scope and it would be way off.

My solution was to use a barlowed laser collimator, as this simply ignores many of these flexing issues. Only then did i have stars similar to when i originally received the scope.
Now i never took any flats during this process as i noticed the issue on my first attempt at focusing on, but maybe it's possible poor collimation could cause this? It does look a bit extreme though, but... Are stars looking the same in all 4 corners?

[alacant]

On 1/4/2017 at 21:00, toxic said:

back and collimated

Hi. JTOL; if collimation has been ruled out, then it could be an uneven light source. Try a different source? Next, the camera sensor?  HTH.