[The_bluester (Paul)]

The reducer/flattener for the ED72 is actually the ED80 one, but for some reason they used an internal thread on the ED72 focuser drawtube versus an external thread on pretty much everything else they make with a 2" drawtube. Meaning the reducer does not just screw on to the focuser like it does on the 80mm.

You can screw a 2" nosepiece into the reducer but with the compression fitting (As you are using to attach your diagonal) you cant quite get enough focuser in travel to achieve focus with proper reducer to sensor spacing. I modified the compression fitting to shorten it and get it to focus but the nose and comression fitting give tilt issues (Different tilt every time you took it apart!) so I had a threaded adapter made which is M54 male on one side (To go into the focuser drawtube) and M56 male on the other to go into the reducer with a narrow shoulder.

Skywatcher have now released an adapter much the same, IMO they should have had that ready when the scope was released. Mine is off being modified at the moment to accept an M48 thread filter cell inside it as my camera really benefits from a UV-IR cut filter and it is a handy way to hide it up in the drawtube where it does not complicate sensor to reducer spacing, just a slight change in focuser position.


Give me a bit and I will put up a pic.

Edit, pic added, all you can see of my adapter is the knurled shoulder between the drawtube and reducer.

I will also add, if anyone else gets one made, take careful measurements of if you can, get your focuser to whoever is making your adapter. The drawtube is to an M54 thread what a cow is to a paddock, not very much the same at all. Some of the Skywatcher fittings are astoundingly poorly specified. Making the adapter to M54 meant Josh on these forums ended up remaking it for me (For which I thank him) as the "Right' thread is so loose a fit in the drawtube I put a couple of wraps of teflon tape on it for fear of popping the threads if I tightened it a bit much, the original compression fitting is much the same in fact.