Strange Screen Artifacts with 294MC - Any Ideas for the Cause

[GaryS]

Hi Folks:
I was attempting a straightforward EAA image of the Medusa Nebula. This was with an ASI294MC camera, live stacking in SC at 20 second images and a gain setting of 400. Appropriately-captured Master Dark was being applied but no flat.

So, you can see a hint of Medusa beginning to come up but notice the black dots in the star field. These I have no idea what they are. Its an early image which I tried several times and finally aborted after I failed to notice the splotches when I did a short stack in The SkyX. The Histogram was wacky as well with the color curves bent almost horizontally. I fought nobly but was unable to get any peaks to work the histo from unless I increased the offset (brightness) way higher than the value of 30 that the camera uses.

So, for now, it would be helpful if anyone recognizes the phenomenon shown and can explain, or even, speculate on the cause. Thank you for any ideas or explanations!
Cheers
Gary

Medusa Problem.jpg (649.78 KiB) Viewed 1179 times

[admin]

Hi,

did you have dark frame subtraction turned on in SharpCap (possibly using a frame as a dark that wasn't a dark frame at all?) That would be my first guess that you are using a different light frame as a dark and the black specks are where the stars in the 'dark' frame are being subtracted.

Check that the 'Subtract Dark' control for the camera is set to 'None' - set it to None if it is set to something and that should fix the problem.

cheers,

Robin

[GaryS]

Thanks Robin. That sounds like a possibility but I thought I had a proper dark from that night selected.
Gary