Quote:
Originally Posted by Lee
Thanks - I pulled apart an old Cheshire to get a sight tube... will try it on the weekend... I was reading about offset secondaries a while ago, all seems a dark art!
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It's pretty straight forward. First you need to center the spider so make sure the four vanes have the same length and the secondary holder is centered in the tube looking from the front.
Second place a piece of white paper (A4) in the tube opposite the focuser then move the secondary sideways, up and down the tube and tilt it until you see concentric circles and the gap around the secondary shape is the same all around. The secondary shoul look like a circle and the reflection of the primary also.
That should get you in the ball park.