Starfield Optics 3" Newtonian Focuser Rack and Pinion

If your Newtonian is carrying a coma corrector, filter wheel, and a full-size camera, the focuser becomes a structural part of the imaging train—not just a convenience. This 3" rack-and-pinion unit is built for that role: a large clear aperture, a rigid drawtube support system, and a geared drive that keeps focus repeatable even when the payload is substantial. It’s a strong choice for fast Newtonians and imaging builds that have outgrown typical 2" focusers.

What you get (and why it matters)

Geared rack-and-pinion drive with “no-surprise” movement
The drawtube rides on a bearing system while the motion is driven by a helical pinion. That separation between support and adjustment is specifically intended to keep the drawtube from shifting under load—useful for maintaining collimation and field sharpness as your camera train gets heavier.

Dual-speed focusing for critical stars
A 10:1 micro-reduction lets you sneak up on perfect focus without overshoot—especially handy at f/4–f/5 where the critical focus zone is tight.

EAF-ready motor interface
This focuser provides a 34 mm shaft diameter motor interface on the focuser side, making it well-suited for adding an electronic focuser motor (such as a ZWO EAF) using an appropriate bracket/coupler solution. The ZWO EAF system is designed to mount to a wide range of focusers via a bracket kit.

Fitment notes (Newtonians)

• Designed as a Newtonian focuser with a flexible base intended for tubes ~225 mm diameter and larger.

• Requires a tube cutout sized for a 3" class drawtube/light path (see specs).

Included connections

• Eyepiece side: 2" + 1.25" (compression ring)

• Imaging / thread side options: internal M78x1 / M68x1 (female) and M74x1 (male) threads are provided to build a fully threaded imaging train (useful with M68 correctors).

• Adapters: 2" and 1.25" adapters with compression rings; the 1.25" adapter includes a 2" filter thread.