JTSAN An example of the EAF after a completed AF. Not really a V curve, right?
The screen capture that you showed indicates that either (1) the grub screws on the flexible coupler are loose, or (2) your step size is way too small.
Check to make sure that the flexible coupler is not completely stuck when you move the EAF step position. In your case, I would try moving manually by 1000 steps at a time to see if the focus changes. Remember that when manually focusing, the ASIAIR uses the fine and coarse step sizes instead of the autofocus step size.
The step size should be about 1/4 to 1/2 of the Critical Focus Zone (check Google). If the math is too hard to handle, first loosen the flexible coupler. Now try to manually turn the focuser shaft. When a star is in focus, you find find that as you turn the shaft from intrafocus to extrafocus, there is a zone in the middle (the diffraction zone) where there is no apparent change in focus. The Bhatinov mask will barely show a change. That is an empirical amount of the Critical Focus Zone.
The EAF moves 5760 steps per revolution. So knowing how much the CFZ is, you can set the EAF step size.
Remember that during AutoFocusing, the ASIAIR uses a different step size than the usual step size. It is located in the Auto Focus menu of the Focuser settings window.
Your current step size appears to be about 6 steps. That is way too small even for a typical small refractor, much less the focusing shaft of an SCT. It probably should be in the region of 30 to 300. Again, you can set it by just using the CFZ instead of fiddling around trying to find the optimal EAF step size.
Be sure to lock the grub screws of the flexible coupler back.
Once the step size is dialed in, you can then do a U curve (as you noticed, ASIAIR does not use the hyperbolic V curve, but instead uses the less sensitive parabolic U curve -- that is why you are better off focusing manually with a Bahtinov mask).
If the step size is just right, you will find that there are about 2 to 3 steps where the star sizes (the dots in the ordinate of the graph) don't change much within the bottom of the U curve.
If there are more than 5 steps (dots), try increasing the EAF step size, and decreasing the EAF step size if there are fewer than 3 steps.
The other thing you need to do with the ASIAIR "autofocus" is that the OTA needs to be in pretty good focus even before you start the ASIAIR "autofocus" process (use a Bahtinov mask). It really is not "autofocus" but a fine adjustment tool as temperature changes.
Chen
