To facilitate comparisons between pictures with different spacing I've been slightly defocussing to make the little "O"s in a manner analogous to collimating on a star, but it occured to me I have no idea whether there is theoretical support for this. I have noticed that if the scope is collinated, I get nice symmetrical O's in the middle irrespective of spacing. The O's are fat on the center most part of the circle if the spacing is very short and toward the outer part of the circle if the spacing is very wide.
Does this make sense? Based on my results so far I'm about to spend $30 and $45 shipping for a 3mm extension ring only available from Germany.
Edited by John Tucker, 09 October 2019 - 04:34 PM.