Auto Guiding a Planewave L-350 mount running in alt-azimuth mode

[Charlie Miller]

I am researching the  use of a spectrograph on an PW L-350 + CDK14 system.  The spectrograph relies on PHD2 to keep the target star precisely centered on the slit.   The L-350 in question is running in alt-azimuth mode and I am concerned that PHD2 cannot autoguide an alt-azimuth mount.  The scope is equipped with a de-rotator but not sure that would matter.  Additionally, the L-350 mount does not support the ASCOM MoveAxis() command, so another concern PHD2 won't be able to auto guide the L-350.

Charlie

[Bruce Waddington]

Take a look at this thread from just a couple of days ago:

https://groups.google.com/g/open-phd-guiding/c/_xVUNIp7zY0

Maybe you two should work together on it.  Pulse-guiding by PHD2 doesn't use the MoveAxis() function - pulse-guide is a separate function in the API.  We know that the L-series mounts can be guided, many, many people are doing it.  But of course, they are also using wedges with the mounts.

Bruce

[Charlie Miller]

Bruce:

Thanks for the response.

The issue is pulse guiding an alt-azimuth mount.  A pulse to move the RA motor in equatorial mode doesn't move an alt-azimuth mount in RA.

Does PHD2 do the calculation that converts a pulse in RA to a pulse in azimuth AND a pulse in altitude?

I assume PHD2 asks the ASCOM driver if the mount is in alt-azimuth mode.

[Bruce Waddington]

PHD2 doesn't explicitly support alt-az guiding so it doesn't try to convert RA or Dec commands into Azimuth/Altitude adjustments.  That can't even be done using the pulse-guide command because the ASCOM standard specifies that pulse guide directions are east, west, north, or south.  PHD2's responsibility is to transform from the camera sensor coordinate system into the east-west-north-south coordinate system.  That happens during PHD2 calibration.  I don't have any way to know what the PW driver or mount firmware do when handling pulse-guide commands when the mount is in alt-az mode and whether the behavior changes in the presence of a rotator.  My reason for suggesting the experiment was to try to shed some light on these questions.

Bruce