[The_bluester (Paul)]

The 8" RASA apparently has a different focuser mechanism to the rest of the range (If it works, I would reckon it might be the first of many. I suspect it replaces what has amounted to a simple sleeve sliding on grease up and down the central baffle tube with a linear bearing to eliminate the mirror flop endemic in the rest of them) but the visible bits of it still amount to the same thing, a threaded shaft that protrudes through the rear cell and the focus knob is actually just a brass nut, secured in bearings that keep it in a fixed position in the rear cell so turning the nut moves the shaft (And mirror) up and down the baffle, if you can call it a baffle in the RASA given they have no secondary mirror or visual back on the rear cell, mirror support tube?

So far it is making focus a lot easier, for manual focus you can just pop on a Bahtinov mask, run the mirror towards the rear cell a few turns to go past focus then with looping exposures step it to focus progressively. The step positions seem to be repeatable all the way down to single steps, which by my workings are mirror movements of under 1 micron at a time. It is probably down near the limit of accuracy of the focus shaft thread. Edited to add: The focus motor is 1000 steps per revolution of the focus knob.

In short, it looks like money well spent. The only thing that would be handy for it would be a little hand controller box if the scope was being used visually as I am not using a Celestron mount. If it comes to that I might see if I can cobble something together that will work with an Raspberry Pi or similar but for imaging it is a non issue. There were some issues with the ASCOM driver which seem to be resolved now, when I first tried it, big focuser moves would crash SGP and I did have some issues with APT as well, though a USB cable change seemed to sort that. I might have to try the other cable again and see if the driver update has fixed that.