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Hi,

I use a thin circular baffle over the secondary hanging off the spider body. I make the hole big enough to illuminated the required field and the outside diameter big enough to vignette the far side of the tube from the field. Either 2/3mm Al or an old CD will do. I cover it with black felt as well. It works well with only a small diffraction effect.

Carl Zeiss used a circular baffle extending down from the spider body over the secondary. The front of the baffle was as far down as needed to only see the primary from the field and a hole was machined into the side facing the field. Ideally you need a conical swing of the cutter for the hole. That could be achieved with a router on a overhead pivot. See Patrick Spielman Router Jigs and Techniques for a clue.

Cheers. Andrew.

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Andrew, I'm having a tough time visualizing this. Do you have any images? - j

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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)

Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan

Facts are stubborn things.

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