I am uncertain of the quality of my Ha and Sii flats. The OIII seems acceptable. All three are Astrodon 50 mm round unmounted 3nm. All Astrodon LRGB flats are OK. System specs: FSQ-106, Gemini Rotator/Focuser, SBIG FW8G-STXL Filter Wheel, SBIG STXL 11002 camera, flat illumination provided by Alnitak Flip-Flat. An image of each NB flat is attached. The Ha and Sii don't have the classic smoothness and boundary. I received an exchange on the Ha filter but it didn't fix matters. I changed slots on the Ha filter and it helped a little bit - moved Ha to slot 6 and OIII to slot 5. Previously all I had for Ha was a bright arc. OIII was unaffected. What can you advise? Perhaps nothing is wrong and the flat is accurately portraying my optics. But why only Ha? Thank you for your assistance. Alan P.S. I also tested Ha in slot 1 - no improvement.