The Monorail M117 has an M117x1 thread on the telescope side. The thread fits perfectly on RC/Ritchey-Chrétien telescopes with an aperture of 10" or more.
- Additional threads: M77x0.75 internal thread on the focuser tube and M74x0.75 external thread
- Short design: overall length from thread to 2" connection only 83 mm
How the MONORAIL focuser works and its advantage over Crayford focusers:
Instead of small ball bearings, as in Crayford focusers, a solid stainless steel rail provides the bearing and also the lateral fixation.
The disadvantage of ball bearing Crayford focusers: The small ball bearings of the Crayford focuser are stressed when clamped. Since the clamping screw is not exactly between the ball bearings, one pair of ball bearings is subjected to greater stress. The result is tilting and blurred stars in one corner.
The advantage of the MONORAIL principle: the ball bearings are replaced by a stainless steel rail that is permanently connected to the extension tube. This prevents any twisting. Only the lateral guidance is still provided by ball bearings. However, these bearings only fix the lateral position and no longer have to absorb any load.
The extension tube is fixed in place by a clamping screw that is precisely centred on the top. This ensures that the entire structure is evenly loaded. There is absolutely no twisting and the extension tube remains 100% in the prescribed position.
The lower centre screw is used to adjust the friction (friction resistance) only.
TS Optics is a brand of Teleskop-Service.
