In order to do the remote focus from the PC, I made a focus motor.

This will be controlled by a Focuser USB interface from Pierro - Astro, ASCOM compatible.

A stepper motor in the Nema 8 format, equipped with a planetary gearbox (ratio 5 to 1), will drive a toothed ring integral with the focusing ring of the lens, via a synchronous belt.

This motor will be housed in a support fixed to the lens retaining rings.

Although the position of the MAP is saved in the interface driver, in the event of a problem, and in order not to risk damaging the helical ramps of the lens, the toothed ring is secured to the lens by six pressure nylon screws, allowing the crown to slip if the ring comes to a stop.

The motor housing

This was machined in Alu 2017A.
The gear motor will be fixed to the cap.
The belt will be tensioned by two bearings coming to press against its back, the pivoting of the cap in the support thanks to the circular buttonholes will regulate the tension.

A Tiny XLR 4 plug has been provided in the motor housing for connection to the electronic box.

Make way for photos ...

The electronics box

The electronic assembly has left its original case to join a Hammond case in Alu cast iron, drilled and engraved for the occasion.

Conclusion

I can now focus from the PC ! And with the Live View, it's really comfortable. The main advantage is to avoid motion blur when the focus is done with the fingers on the lens, we do not really know if it is not in focus, or if it is moving !