chaosnix68 My problem is the focus slips after the temperature changes maybe you don't understand my use case.
One thing that you can do to work around the ASIAIR's lack of ability to pause live stacking is to do an experiment one of these nights -- it does not have to be fully clear or transparent, or wind-free night -- as long as you can see the brighter stars through a Bahtinov mask.
Note down the temperature (best to have a temperature sensor taped to the OTA between the objective and the focuser) and the EAF setting when in focus.
As tempearture changes, refocus and note down the EAF setting again.
Now, this is most important (to work around backlash from the EAF) -- notice which direction the EAF is moving as temperature goes down.
Lets say the EAF count goes down as temperature goes down, start with the EAF at some high value. Achieve focus by only reducing the EAF count. If the EAF needs to move up as temperature goes down, start with the EAF at some low value. I.e., from the beginning to the end, only move the EAF in one direction.
This way, through the night, the EAF is moved only in one direction (notice that the ASIAIR autofocus also tries to move the EAF count in one direction while autofocusing -- but it does not always do it to match the temperature change).
Once you have established a table of EAF vs temperature, notice that ∆EAF/∆T is pretty much a constant for at least many degrees C of temperature change. I.e., EAF vs T curve is locally linear, and you will be replacing the curve with a piecewise linear approximation.
In the future, just use this to table to blindly nudge the focuser as the temperature changes as the night goes on. Your focuser will need to have a moderately small image shift when focusing -- small enough for the stacking program to track.
I use this even when I never use live stacking, albeit I pause an autorun to make the EAF nudge. But it saves me lots of time refocusing over the night. (My FSQ-85 is especially sensitive, mostly because it has such a small spot diagram to start with, and requires an adjustment every 0.5ºC to maintain that small spot size, and I am OCD about tightly focused stars.)
If you use filters, you can also calibrate the ∆EAF for all the filters that you have. When you change filters, just use the table to adjust the EAF; no need to refocus when you change filters (another function that is missing in the ASIAIR).
Chen
