I've updated the charts in the OP (now ~1 year, 350 autofocus runs at night). The temperature data now slightly favors a weak quadratic fit (but I'm still showing a linear). The temp ranges from 20F to 70F. I've also examined focus sensitivity for different systems against seeing (1.5 to 3 arcsecs, f/2.2 to f/10 setups). For ease of understanding, I have attached two graphs, one showing a CFZ perspective (microns), and the other using an EAF quality focuser (5760 counts per revolution) combined with a 750um focuser thread pitch (resulting in focus counts). In case it's not obvious, f/10 or f/7 setups won't need Adaptive Focus Control (AFC for you football fans). In good/best seeing, f/4 might benefit. In all cases, f/2 and f/3 need AFC. Those of us with f/2 or f/3 systems know intrinsically what the charts are saying; the current focus adjustment controls (think scheduler, time/temp deltas) do not suffice. I've also attached a temperature chart from this month to support that assertion.

This month, I used a stand-alone program to manage an autofocus "integrator", and manually offset focus between exposures as temperature and elevation changed. Manually intensive, but the results were very satisfactory! There appears to be no Ekos "gotchas" for updating focus between exposures. Adjustment could be coexistent with download, dither, or exposure delay timing. I was easily able to maintain focus in my f/2.2 rig as temperatures rapidly changed. One good seeded autofocus and then occasional updates between exposures will keep focus well managed. Only 1 autofocus needed per target!

So a couple of thoughts. My 7 night January run had some bad seeing in it. Autofocus has difficulty when HFR readings are bouncing all over the place. This adds to spread in the logged data. Linear autofocus tends to pull up short of the bottom of the V curve in bad seeing, especially if the last HFR reading (averaged or not) is marginally higher than the prior HFR reading. Getting one good autofocus result, followed by AFC updates, seems like a better approach to managing focus than risking N funky autofocus results. Bad autofocus endings skew the log data; not sure how to adjust for that yet. Finally, while I started this idea thinking that a seeded autofocus was the goal, it now seems clear that AFC between exposures IS the goal. A seeded autofocus start is still desirable, but realized AFC between exposures is a "can't live without" kind of feature for f/2 & f/3 systems! So work will continue.... cheers, Doug