Re: [ATM] Questions about string scopes

[Stephen Russell <smr@prominence.net.au>]

Hi Mel and Dale

> Adjust the truss pole lengths.   Mel Bartels

Very true, but probably a little cryptic for someone who hasn't figured 
out string scopes yet.

Dale, adjusting the length of a truss pole is not impossible. The trick 
is to get an arrangement that is quick to setup yet be close to 
collimated each time.

Have a look at Dan Gray's design for one approach.

My idea is something similar. Each truss pole is two parts: a short 
piece (a few inches long) with a threaded insert at one end, and the 
main pole. The main pole fits inside the short tube, and has two slots 
that engage with pins in the short piece. The short piece sits on top of 
a bolt attached to the "mirror box". The long poles use ball-and-socket 
joints to attach to the OTA.

Setup is simple: drop the long poles into the short ones, turn them to 
engage the pins, then keep turning until the strings are tensioned. The 
correct position of the pole is marked during initial collimation to 
make this repeatable. I then clamp the ball joint to stop the tube 
rotating during the night.

Caveat: I haven't built this design yet. In the meantime, use Dan's 
design ... :-)

Steve.
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