TS-Optics PHOTOLINE 2.5-inch rack-and-pinion focuser

Telescope-Service has been shipping telescopes for amateur astronomers and astrophotographers for years now. Our goal is to equip these telescopes with first-class focusers, for a reasonable price. Our 2.5" RPA focuser is an alternative with a quality that can be found in the upper range. Many of our TS-Optics PHOTOLINE Apo refractors are equipped with this focuser.


The Rack and Pinion drive system:
A Crayford focuser operates with contact pressure. The pressure of the shaft stresses the ball bearings and also reduces the sensitivity of the adjustment. The bearing of the RPA focuser is also done by ball bearings, but the adjustment by a rack is decoupled. The advantage is that the bearing can be optimized, maximum stiffness is the result. Even at maximum load, the adjustment is very sensitive and jerk-free.

The clamping of the focuser position has also been optimized. No clamping screw simply presses on the focuser tube, but the position of the adjustment is fixed. This ensures that the focus position is held 100%.

Adjustment: Even this construction can become misaligned over time. To help you adjust it correctly again, TS has created a PDF guide that you can download here.


Self-centering 2" and 1.25" adapters
A good force fit is also necessary when clamping 2" and 1.25" accessories. Simple clamping screws would cause tilting. The clamping of the PHOTOLINE RPA focuser takes place centrically by evenly encompassing the complete 1.25" or 2" barrel.

The adaptation of the focuser to the telescope.
The outer diameter of the focuser tapers to 79 mm on the telescope side. Suitable telescope adapters must therefore have an inner diameter of 79.1 mm. In addition, the port provides a groove 5 mm from the stop, which is ideal for clamping. We therefore recommend that connection adapters be fastened 5 mm from the stop edge (thread center). Ideal would be the fastening with M5 or M6 screws.