even reflecting astrographs do have certain amount of glass in the optical path - I mean, the field/coma correctors etc. That is refracting optics - that brings the problems with IR wavelengths. For DSO imaging you risk bigger and bloated stars if not using an UV/IR cut filter...
I think ZWO doesn't add a typical UV/IR cut filter in their cameras as they started as a planetary cameras manufacturer. For planets, it can make sense to have the IR wavelengths to pass so as you can filter the light yourself - either want it - for e.g. Moon imaging with an IR pass filter or you do not want it - you add the UV/IR cut.
But for DSO imaging, there's very, very little use cases for imaging WITHOUT an UV/IR cut filter.
I have mine permanently installed :-)
My opinion: in a color camera meant for DSO imaging there should be an UV/IR cut filter installed right away out of the box, not just AR-AR filter... (or whatever is there).
