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Secondary Size Might Be Wrong - Need Help Urgently

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Posted by Dave Sellors on May 26, 2003 16:43:09 UTC

I've almost finished building a 10" dob (Richard Berry book), my first time doing this stuff. Mirror is 10" F/5, secondary size is 1.83" I laid out optics using Newt 2.5 and did ray trace using Visio. Newt reported everything to be fine (no YES's). The focuser hole location was based on achieving a very thin, almost imperceptible, black ring around the primary when looking at the secondary mirror through the focuser.

I now have just read "treatise on newtonian collimation", which seems to say I should have a somewhat thicker black ring.

What should I do ? Advance the mirror toward the secondary and hope focuser height can absorb it, or should I get a 2" secondary.

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