Plate Solving with Celestron CPWI ASCOM interface

I am using he new CPWI telescope control application from Celestron and its ASCOM driver to interface with SGP (V3.0.3.169). In the latest release of CPWI (V2.2.3), Plate solving fails to converge when I select a Center Here or Center on Target function. Each SGP plate solve move command causes CPWI to command the mount to move away from the last position and do a slow approach in RA and DEC to the new position. Since there is always a small error in the pointing model, SGP only gets to within 100 - 200 pixels of the desired position after 5 tries.

Does SGP always issue a GoTo command for each error correction during plate solving, or does it nudge the mount when errors are somewhat small (say within 1000 pixels (~500")? Celestron says the problem is not theirs… If you issue a GoTo position command on each plate solve error, then CPWI may never move the mount where the error will go below the desired value (in my case 15 pixels). Note to that the older version of CPWI (2.1.25) will converge to near the desired centering position in SGP. I have tried to explain this to Celestron, but they don’t have an answer…

Nudging works well from PHD2 guiding, both with autoguide and manual guide modes.

I am trying to solve this issue and determine if it is CPWI or how SGP plate solving centering works.

Mark W.

Celestron CGEM II mount
Lenovo Thinkpad 11e with latest Windows 10
CPWI 2.2.3

SGP always issues GoTos. We do not nudge. The closes we get to nudging would be when using “Target Offset” for the Sync behavior. In which case we still issue GoTos but adjust the slew with an error offset determined by your last sync. Typically you should not have to use Target Offset…but might be worth a shot.



Thank you for your prompt reply.

I will give the target offset setting a try for synching.



Interesting you are having this issue. Did the offset work? I’m having the same problem. It worked great the first time I tried it then Plate solve started bringing up an error after that. I will try and duplicate it again this weekend