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Paul, at that FL, are you binning the guide cam?. At over 2m, I bin 3, much shorter exposures, works fine, but sightly out of focus, cause otherwise stars are a bit blocky. At bin 1 or 2, the stars are smoother, but guideing is more unstable due to extra noise with the same exposure times.
I found that slightly out of focus can indeed help, but it depends on the guide image scale. A single block star is rare but fine focused, its when it suddenly becomes 2 pixels it gets nasty, jumps all over the place and defocus is required, albiet at slightly reduced but smoother acuraccy overall. Oddly, a multipixel (shorter FL, or non binned) star can sometimes do with defocus too due to dancing pixels appearing and disappearing on the edges, moving the centriod.
Why does flexure require "sorting" again with the QSI?, doesnt it become irrelivant?.
Why do you need a spacer to adjust focus, cant you slide the guide cam up and down?, or, doesnt the QSI also have a focus adjusting ring?.
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