Crayford focuser

Instead of the rack and pinion, they have a smooth spring-loaded shaft which holds the focus tube against four opposing bearing surfaces, and controls its movement.

The Crayford focuser was initially demonstrated to the Crayford Manor House Astronomical Society, and then descriptions were published in The Journal of the British Astronomical Association (February 1971),[1] Model Engineer magazine (May 1972)[2] (with full constructional plans), and Sky & Telescope magazine (September 1972).

John Wall decided not to patent the idea, effectively donating it to the amateur astronomical community.

This trend picked up steam as commercial Crayfords, while being relatively inexpensive, proved to be superior to most rack-and-pinion devices.

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.