[bojan]

To prevent the effect of backlash in helix focuser, I am trying this idea.. there is another identical spring (from Bunnings, of course!) on the opposite side of the tube (in principle, three springs would be better, but I didn't think of it when designing the saddle for this lens, so.. two should be good enough).
It is easier to do it on MTO-1000A (Rubinar is more difficult, there is less space available for those additions).

Edit: this works OK it seems.. it is now much easier to get the focus right (with help of live view)