Quote:
Originally Posted by AstroViking
That's an interesting collection of adaptors and tubes there.
The ZWO website talks about needing 55mm of backfocus - you've got a lot more than 55mm.
Where on earth do you measure from?
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To tell you the truth I'm no physicist so I used the tried and true priinciple of "suck and see".
As I understand it, the sensor plane has to be 420mm (scope's focal length) away from the objective. I could have got away with less extension if I'd racked out the draw tube a bit more but I just cobbled together something from what I had - works for me.
The 55mm is if you're using the flattener.