The Crayford focuser is a simplified focusing mechanism for amateur astronomical telescopes. The design replaces the complicated rack and pinion drive normally found in this type of device with a smooth spring loaded shaft which holds the focus tube against four opposing bearing surfaces.
Crayfords are popular among amateur telescope makers as they are easy to make without any high precision machining, yet provide precise focusing with no gear slop or backlash. They are also made in a variety of designs by companies specializing in amateur telescope supplies.
The Crayford focuser design is reminiscent of the Dobsonian design for telescopes, since instead of precision machining, it relies on geometry to preclude any wobble or backlash.
The Crayford is similar in appearance to a Rack and pinion focuser, but has no teeth on either the rack or the pinion. Instead, a round axle is pressed (for example by a spring-loaded or thumbscrew-tightened piece of PTFE plastic) against a flat on the side of the focuser drawtube, relying only on friction to move the drawtube as the axle is turned.
This also presses the drawtube against a set of four ball bearings against which it moves smoothly with minimal friction. The pressure exerted on the axle can often be adjusted for smoothest operation, and the drawtube may be locked in position to support heavy eyepieces or cameras.
Subsequently, variations on the Crayford concept have emerged, e.g. a helical Crayford where the drawtube is pressed against four tilted ball bearings, and focusing action is accomplished by rotating the drawtube.
Skywatcher Dual-Speed 2” Crayford Focuser for SCT Telescopes
A high quality CNC machined 10:1 dual-speed focuser designed as an upgrade to Schmidt Cassegrain Telescopes. Accepts either 1.25" or 2" eyepieces. Provides an exceptionally smooth focusing operation with the utmost precision, with the aid of its fine-focusing facility. Indexed Drawtube
This high-quality Crayford uses a sturdy brass ring to hold eyepieces securely in place so you get the best images. This focuser accepts both 1.25-inch and 2-inch eyepieces and features a micro-focus knob for precision
MoonLite Model CF Refractor Focusers.
The CF model refractor focuser is a 2" format crayford based unit designed to fit most popular refractors. It features a modular design allowing the user to pick the exact configuration of the focuser to match their telescope's requirements.
They are made in the US to exact standards and feature MoonLite's highly polished hard anodized aluminum surfaces. All hard-anodized surfaces ride against stainless steel bearings and shafts, providing extreme smooth operation that will never wear out.