Thursday, May 6, 2010

My 8" F/4 travel scope: Focuser

I hate making focusers and am too cheap to buy. This is a push-pull Crayford: the draw-tube moves against PTFE runners. The draw tube is made out of super-cheap PVC conduit (something like two or three dollars for 12 feet). Unfortunately, the conduit's inner diameter is significantly more than 1.25", so I lined it with PTFE strips, which I sanded down to fit eyepieces.

The focuser's tension is adjusted by having a piece of metal glued on its bottom part (with JB Weld), and with a thumbscrew bearing against the top part, and with PTFE on it, on one of the three posts.

Here is a picture of the focuser board at an early stage in the production. The elongated hole is for the secondary stalk.

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