ckoos My autofocus setting is to run after a 3c change in temperature, but this log says it ran after a 5c change.
There has been a long standing bug with the autofocus intervals (ever since ASIAIR released autofocus). It almost appears to round one number up, while rounding the second limit down.
That being said, you probably could double the EAF step size that you are using for autofocusing. It is staying in the critical focusing zone for more steps than necessary.
You are lucky that you even only need to autofocus every 3ºC. All of my telescopes need to be auto-focused more often than that -- the most sensitive of my scopes is the FSQ-85; but part of the reason is due to how small the in-focus spot size is, so you notice out-of-focus condition very early).
Just recently, I added the focuser kit (the one with the tracking sled) for my Askar FMA230 from deepskydad to use with a ZWO EAF. I had been manually focusing the FMA230 before that.
After spending two nights just making measurements, I found that it is moving the drawtube by 0.65 µm per EAF step (if memory serves, I am not looking at my notes right now), which corresponds to a critical focus zone of +/- 40 EAF steps.
The temperature gradient (around 12ºC) is about 45 EAF steps per degree C, while the critical focus zone. Both these numbers are large compared to a typical-use case with the EAF coupled to a rack and pinion focuser, where I see numbers that are more in the region of 2 µm per EAF step.
A focused FMA230 image will fall out of critical focus in 0.9ºC. (By 3ºC, the stars are visibly bloated.) If you maximally pre-bias the focus position, it will still fall out of critical after 1.8ºC.
My strategy on focusing with the ASIAIR is to use a Bahtinov mask to focus before starting an autorun sequence. I then use the temperature gradient to manually step the EAF by pausing the autorun when the temperature change exceeds a threshold.
With my FMA230 set up, I simply watch for a 0.4ºC change in temperature, and blindly change the EAF by 18 steps. Wait a second or two, and resume autofocus.
With the FMA230, I also "pre-bias" right after focusing by 9 EAF steps towards the colder temperature, so that I am not smack in the middle of the critical focus zone, and that gives me some extra headroom of 0.2ºC in case I am not monitoring the temperature at the time.
I was watching this strategy the last few nights with 300 second exposures using narrowband filters, collecting the star size of each frame; and it is working pretty well with this particular OTA over multiple degrees of temperature change without having to refocus with a Bahtinov mask or a V-curve.
Even if the temperature gradient is off by 10%, it will take many degrees of temperature change before I need to do a measured refocus.
Many programs allow you to set a temperature gradient so you don't have to waste time reestablishing the V-curve that often. But ASIAIR does not have that function. Even so, pausing an ASIAIR autorun to blindly step the EAF before resuming the autorun again only wastes some 15 seconds every couple of 300 second frames.
Chen
