Hi bdavis. I think you're driving toward a much more complicated automation regime than what I've suggested (i.e. elimination of autofocus). I fear that would be very unlikely to ever get implemented (unless you write and test it yourself). What I have suggested in this thread HAS been implemented at multiple large observatories. I know this because I personally worked on the temperature and elevation compensation model at the Large Binocular Telescope, and a similar strategy (lookup tables) was employed at Keck where I worked before LBT. I have used the data I posted for my own f/2.2 RASA 11 (highly sensitive to focus) and it works great. Whether I can convince you of the suggested approach is moot. The proof is in the results and is available to everyone. For the unbelieving, a better question might be: "how and why could this improvement approach possibly work?". So let me try and address that just a bit more.

The temperature component works because the dominant error we're beating down is structural (lateral shift of optics due to changing temp of the OTA). The next component (residual of the temp function) has complex / multiple underlying reasons, but airmass (target el) empirically correlates against the residual to beat it down. Together, these two available variables get us within the ball park to improve focus management. The key to why this simplicity works is that we're NOT doing a one-time blind position update. We're not replacing the closed loop autofocus routine. We're only "seeding" the autofocus loop's start position. The autofocus loop is still responsible for resolving best focus position. Therefore, all the discussion about spread and CFZ size is misdirected. Ok, now to the next suggested higher automation level (updates between exposures). In that scenario, any position update would use the function outputs as integration OFFSETS from the base position determined by prior autofocus. Those offsets are small and driven by trendline direction. Here, the spread isn't as important as having the trend SWAMP the spread so the direction and magnitude keep us within the CFZ and REDUCE our need for another autofocus run. I mentioned to Bart that I'm not sure I would trust a blind update for a large elevation difference slew (and I still believe that). Bottom line: The work needed to do a one-time blind offset and ELIMINATE autofocus runs is well beyond the scope of this thread. So, whether or not I've convinced you, I hear you. I suggest if you want to discuss a "predictive focus tool" that eliminates the autofocus loop, please open a new thread for that topic. I'd like to keep this thread within the bounds of improving and reducing the existing autofocus loop interface (as opposed to eliminating it). Cheers, Doug

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