strange artefacts help

[PNJ]

Hi All

was imaging M81 last night, using a 8 inch edge HD with 0.7 edge reducer.

When finished my imaging run, i did the usual flat calibration and it seemed ok,  until i stretched the image and the result as photo

has anyone seen theses artefacts before,  My typical raw showed the usual doughnuts etc, and my flat images looked perfectly ok, when applied the flats, everything still seemed ok

until the stretch.

was wondering if its a fault on the reducer unless someone can put me right

cheers

paul

[nmoushon]

Almost looks like a water/dew drop. But can't say for sure. Very peculiar.

[iksose7]

Never seen anything like that before   shame as well because that looks like some nice data. 

Only thing i can think of is dust. Or UFOs 

[Stargazer33]

MMMMM...doughnuts. 

[Mark72]

I had something like this, it's when flats are not correcting and only magnifying the doughnuts.

Probably something shifted, may be you can try flats again or use old ones - whatever works.

Mark

[PNJ]

Hi

think i discovered the problem, My Reducer had a large finger print across the lens, this might have been the issue.  However i have taken fresh flats and gonna try

paul