A friend of mine - Dominik - has donated focuser from his FSQ106ED (which was replaced by Starlight Instruments 3,5" focuser).

As I had some minor issues with my 106N focuser, I decided to try replacement with slightly heavier and larger ED focuser.

Another friend of mine - DaroMitek ( http://www.astromitek.pl/) made on a lathe a 40mm long connecting ring. This length was necessary, as the larger EF focuser rack rail does not fit into smaller diameter 106N tube. As a result, the backfocus was shortened by some 26mm as compared to the original version.

Robofocus motor has been attached to the microfocuser knob using tried and tested approach of quick-release clutch and bracket (see another gallery). Now, all my scopes have Robofocus motor attached by quick-release system to the right of OTA, so the focuser movement direction is maintained between scope changes. This simplifies greatly imaging setup swaps for my balcony observatory - all I need is to swap configuration files for MaximDL and CCDCommander (manly image scale for plate solves) and FocusMax (focusing curves).

Initial results compared favorably with my past experience. Most importantly, the additional gearing from microfocuser planetary drive provides very fine focusing steps of ca 0,9um per step - so for the NCFZ of ca 26um I now have movement of 30 steps. Far more positional precision is possible - previously it was less than 2 steps in the CFZ. Also, much less torque is needed from the motor, so no chance for skipping steps.

BTW 1 - here for the second time I have removed the brass collar from Robofocus gearbox shaft - which proved in the past to be another source of slippage in the focusing system. Now, the clutch is attached directly to the steel shaft with set screw pressing on the indented portion.

BTW 2 - the CAA provided with the new focuser was hopelessly wobbling - no surprise that the first owner was experiencing huge problems while imaging with it. A simple adjustment cured that issue (see Don Goldman - Astrodon pages for details).