@matt s#53961 Regarding the Guide Rate issue, I don’t understand the ‘marriage’ between the AAP and my CPC mount, ie which dominates the other? Can you explain?
There are two general ways to do autoguiding. One is to guide using the ST-4 protocol, and the other is to go through the serial command (RS-232 or USB) protocol, and this second method is normally called "pulse guiding."
Unfortunately, when you use the ST-4 protocol on the ASIAIR, you cannot use any other mount functions (slewing, GO, etc) from the ASIAIR app. Other software allows you to guide with ST-4 and still control the mounts other functions. With ASIAIR, you can only choose to use your mount, or no mount at all (i.e., choosing "On Camera ST4" as the 'mount").
With the ASIAIR and its guide bug, you are stuck with either not being able to guide, or not being able to GOTO. So, switching to using ST-4 is really not a sloution either when you use ASIAIR.
The usual way to do pulse guiding is for the computer to
(1) switch the slew speed of the mount to 0.5x or some slow speed (or select the mount's guide speed),
(2) send a slew command
(3) set a software timer to time N milliseconds
(4) after the N milliseconds, stop the slew.
Basically, this will slew the mount at the selected speed for N milliseconds.
N is determined by how much correction is needed (during calibration, PHD2 that ASIAIR uses determines the number of milliseconds needed to move the mount by 1 pixel, and relating pixel to arcsecond (recall that 1x sidereal rate is 15 arc seconds per 1000 milliseconds of N).
When PHD2 discovers that the guide star has moved by P pixels, it computes the number of arc seconds that P seconds corresponds to, and from the calibration data, figues out how large N needs to be to move that many arc seconds.
Some mounts allow you to send a single command in place of steps (2), (3), (4) above, and let the mount perform the timer. This is actually more accurate, since it does not depend on the latency of the serial commands (perhaps ten milliseconds per command at 9600 baud). But as far as I can tell from my simulator, ASIAIR does not use the more accurate, lower latency commands, even when the better command is available, and keep using the steps (1) through (4) above.
As far as the guide rate is concerned, I am not sure if ASIAIR even uses the guide rate in your hand controller. When you enter the Guide Window in ASIAIR, it warns you that with SynScan mounts, you need to manually set the slew speed to 1x, which hints that ASIAIR is asking the mount to use the slew rate in the ASIAIR, instead of the guide rate in the mount. Many users don't read instructions on the ASIAIR windows since they think ASIAIR is "Simple as 1,2,3."
If you are using the mount in Alt-Az mode, that could also compound the problem since ASIAIR continues to slew in RA and Declination, instead of sending Altitude and Azimuth slew commands. The problem could also be compounded by connecting something like SkySafari to ASIAIR's mount proxy, since SkySafari can also change the slew rate. The ASIAIR mount proxy is not a true proxy -- it mixes the commands from ASIAIR and the commands from SkySafari.
Chen
