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I got an adapter made to mount the ED80 focal reducer on my 72mm (For some reason Skywatcher use an internally threaded drawtube on the 72mm instead of an externally threaded one on the 80mm and some other larger ones)
Josh Bunn on these forums made it for me. I have just packed it off back to him to get an M48 filter thread turned into the clear aperture of it so I can hide the filter up inside the drawtube, in front of the reducer/corrector. Pity I did not think of that when I got him to make it to begin with. If the female thread end of the filter was longer I would probably have just left it between the reducer/corrector and my OAG, but it had not quite one full turn of thread in it so it was a little nerve wracking in that location with the guilder and camera hanging off 0.75mm of thread.
The filter I have is the ZWO IR cut only. I did wonder if a UV cut would also help at the other end of the spectrum but at least for now the camera is finally working in the way I expected. Results on the 72mm were OK but there were a lot of bloaty looking stars and the insane reflections which were obviously somewhere longer wavelength than the cutoff of the filter. I was chasing odd reflections with the SCT too so it might have the same issue.
I am not sure how to deal with it for the SCT if I image with that any more, unless I can find a filter with much longer female threads it will be tough to mount one apart from shelling out for a filter wheel as a step towards LRBG/Narrowband and putting in a UV/IR cut filter which would end up used as a lum filter later on whenever I eventually go mono.
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