hello,
I have been imaging the California nebula and found that there was a large gradient in the final image. I have now taken some flat frames for the setup and found that the gradient was in all of the photos and took up about 1/3 of the sensor space.
I have attached an image of a flat frame to show the issue.
I am currently using a skywatcher esprit 100ed with my ASI 294 MC PRO. Between the two of them are, field flattened, ZWO OAG, 2 spacers and ontology l-enhance filter. I have checked down the objective and can see no issues with the alignment up to the filter. All threads are screwed in correctly with a snug fit, and there are no massive pieces of debris covering the objective.
need help ASAP please.
cheers,
george