[Wavytone]

My MK91 has similar limited backfocus as it has fixed mirrors. I replaced the focuser with a low profile Baader Steeltrack 50mm UNC one from TeleskopService, though doing this involved having a new backplate adapter machined by TS - which was at a very reasonable price I should add. The focuser has a pinion with clutch for a toothed-belt drive and I have the TS motor drive for mine - though currently not using it.

This gave a focusser travel of 25mm. If interested I’ll add a web link to the unit.

This issue for you to sort out is that these low profile focussers all assume the drawtube (probably 65-70mm outside diameter) can fit inside the backend of the scope anywhere from 15-25mm in order to provide the full travel. In my case 15mm.

This may or may not be possible on the Mewlon and you’ll have to dismantle the back to find out.

If the backfocus is close but not quite enough the other solution is to use the primary mirror adjustments to shift the mirror forward. Shifting the primary forward 0.7mm (1.0 screw turns) will shift the focus out approx 5mm.