ts60

 Second time lucky? Not really. The tsflat2 just wouldn't correct so here we are insteadwith the tsflat60. Using the recommended or greater than the recommended sensor distance (tsflat2 = 128mm, tsflat60 = 55mm) with both flatteners does the opposite of what you'd expect; the stars toward the corners get more radially elongated. Oh, and tilt. How do you adjust with an all screw-fit connections? Evidently a tilt adjuster. Oh how I hate refractors... etc.

Anyway, got something like at 54.5mm backfocus. Next, to try 53.5mm, then we'll have a better idea. Certainly at 55.5mm, the elongation was too bad.

ngc6888 crescent in cygnus
veTEC571 on ts60    70x5min @ hcg100

region around sadr in cygnus
veTEC571 on ts60    36x5min @ hcg100