I finally had a chance to test the Baader Ultra-Narrowband H-alpha 3.5nm filter on a night of exceptional seeing. I captured this image with my C11 EdgeHD at f/7 on an iOptron CEM120 EC2 mount. Total RMS was 0.24 arc seconds during the 40 180-second exposures with an ASI 1600Mm Pro at -10c. 30 darks, but no flats or bias.