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Accurate mounting of the focus board
While i'm at it, what techniques do you use to measure that the focus board is mounted and pointing exactly to the center of the UOA? I am presuming I will use two small blocks mounted on the upper and lower rings to support the focus board, probably 1/4 " ply.
I have noted that AstroSystems use a piece of paper wraped around the tube and subdivide it into 90 degree elements when mounting the spider. We would have to use one or both of the rings in absence of a tube.
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