MasterFlatHaSTR

Ha master flat frame - STF stretched in Pixinsight - this was taken after flipping the entire filter wheel assembly to reverse the orientation of the filters relative to the OTA vs. camera. Compared to the un-flipped orientation, the heavy edge ring pattern is greatly suppressed. There is still some vignetting and there is a new, much weaker, radial pattern at much smaller radii. This indicates that there is more than one source of reflection.

40 flat frames at 10.79 seconds using Sequence Generator Pro. Integration time was determined using SGP flats calibration wizard.
Illumination was using an Alnitak Flatman with two layers of tee shirt fabric. This was the exact same method that was used in the previous un-flipped orientation flats.

No bias frames used only Flat Dark Frames - 40 flat dark frames

ORION EON 115mm APO
ZWO ASI1600MM-COOL with a Williams Optics Flattener IV at F/5.75 with Gain - 75, Offset - 40, USB - 60, Temp = -15C