Baader 3.5/4nm Ultra-Narrowband SHO Filter Set - 1.25" Mounted

Baader 3.5nm / 4nm Ultra-Narrowband Filter Set – CMOS-optimized (H-alpha, O-III, S-II) - 1.25" is a midrange narrowband filter (1.25").

Best for isolating emission lines with a mono camera and filter wheel.

Choose filter size around the sensor diagonal, telescope speed, and filter-wheel or drawer geometry. Flats are still required; a filter can improve contrast, but it will not rescue tilt, bad focus, or poor calibration.