MasterLightOIII R STR

Part of the Heart Nebula mosaic with OIII filter Master Light Frame - 30 X 240s exposures

I used 60 DARKs, 60 flats by filter, 60 Dark Flats for calibration. Calibration, Star Alignment and stacking with PixInsight

ORION EON 115mm with ASI1600MM-C with ZWO 7nm Ha, OIII, SII, Lum filters - image capture with Sequence Generator Pro
ORION HDX-110 EQ-G with ORION 70mm/ASI290MM for guiding with PHD2.

There is still a radial gradient pattern as seen in the OIII Master Flat did not calibrate out from the light frame. The same artifacts are not very visible in each light frame. I almost think I should just skip flat calibration and see how it looks. However, the image is better than the OIII master with the unflipped filter wheel. These issues lead to a severe color ring artifact in the SHO composite image.