The TS flattener the TSRED279 is designed for a scope in the F7.8 range, in fact a doublet. That one can be either mounted in a 2" drawtube or can be screwed into a focuser that has a 63mm thread under the top cap, Feathertouch, Stellarvue, and WO 2.5" focuser have this but those are not cheap. Also you can get an adapter to mount it on a 68mm threaded focuser such as used by Zeiss, APM, and Moonlite 2.5" ones.
I have an SVX127D on order from Stellarvue which will get here next month I think. Due to the focuser shortage from Feathertouch (founder passed away and the manager left) I could no longer get it with the FT 3". SV restarted their own 3" focuser production line to fill the gap and reduced the scope price accordingly. However while the SV focuser is a very close match to the FT I already had a 2.5" FT sitting in a box so they agreed to put that on my scope since they already made an adapter to fit between the tube size difference (and reduce the price). So now I will have a 63mm top, and I will be using the TS one which is a close match F-ratio wise and also made for a doublet. The difference between a 3" and a 2.5" focuser, except payload, is non-existent with a scope F-ratio of F8.
Hate to say, the best way to determine in and out is to actually put the thing being used on the scope and try to focus, always at infinity. Failing that, determine the exact infinity focus point using something like translucent (wax?, something) material taped over the end of the focuser tube. You can focus on daylight objects (buildings) at infinity and a projection of the subject will appear on the temporary screen. This is the infinity focus point of the focuser. It's easy to calculate how much in-focus you'll have for a digital camera, you need to accommodate its flange to sensor distance and any depth added by adapters to use it on your scope. However, how it will behave with a reducer/corrector is a question, it depends on the specific unit.
For some more info check out these:
Reviewer is wrong about one thing, Vixen fluorite scopes were serialized in the older green mount days, just not in the current white mount phase.
Edited by photoracer18, 04 August 2021 - 11:02 AM.