I've been looking for a good rotator, that won't cause tilt.
I think using Borg components is an excellent solution.
It consists of the #7352 Borg rotator, which has M57 threads, and then a #7522 and #7528 adapters, to get it to male T2 and female T2 on either side.
It is buttery smooth, rock solid, and seems to keep the imaging train precisely aligned, without tilt.
I measured the total optical length as 25.8mm, but I may not have measured accurately as it should have come to 26.0mm, and usually the Borg components are specified very well. I would assume 25.8mm to 26.0mm.
So if you have an astronomy camera with a 6.5mm setback for the sensor, and a 20mm filter wheel or 21mm filter slider, this still can achieve the 55mm back-focus of the many components (flatteners, reducers, coma-correctors, etc.).
There are no Borg adapters to go M48-to-M48, but they may exist in other brands.
Here is the link to purchase Borg components. Just type in the part number in the search window:
Edited by StevenBellavia, 26 September 2020 - 04:40 PM.