I bought the 36mm unmounted version and fitted this to an empty 2″ filter holder using a 3d printed adapter. Using a 36mm filter was cheaper than the 2″ version – and the ideal size to be used with the new Sony IMX571 APS-C sized sensor (minimal vignetting at F4.65 in my case). I decided on the 3nm because I wanted the tightest passband possible to use on moonlit nights – the majority of the clear nights here seem to fall around the full moon.

I use this filter on a 105mm refractor with a 0.75x Riccardi reducer. The Chroma Ha filter produces absolutely no evidence of a halo or weird reflections, even on the brightest of stars. I have tried with other brands of Ha filters, and they all produce haloes of varying sizes and brightnesses, along with reflections. The stars are also pinpoint in size, making it incredibly easy to remove them in star-removal software, and produce mesmerising star-free regions of dust and gas.

I imaged NGC2264 with this filter less than 90 degrees from an 83% moon and I was unable to detect a gradient in the sub frames – it is literally that good at isolating Ha emissions in the presence of moonlight.

I have since bought the Chroma 3nm Oiii and 3nm Sii filters These filters are a significant investment but what they do is produce high quality raw data that is so much easier to process with high contrast features.