What exactly is a Crayford focuser?

[toc]

Um, kind of embarrassed to ask this, but what is the main difference in use between a so-called crayford focuser, and a rack and pinion focuser?

Ive only ever really used the rack and pinion on a very cheap scope, and then the SCT style focusing systems. (which I quite like)

[ballaratdragons]

Hi Toc,

The crayford is a pleasure to use due to it's smooth motion, no backlash, and the fact that most have adjustable clutches and a lock.

The barrel is driven by bearings and pressure rather than a rack and pinion gear method.

Here is an interesting link for you to read. It explains how a Crayford works, it's history and how to make one. http://www.aqua.co.za/assa_jhb/new/Crayford.htm