View Single Post
  #40  
Old 15-09-2014, 10:20 PM
mithrandir's Avatar
mithrandir (Andrew)
Registered User

mithrandir is offline
 
Join Date: Jan 2009
Location: Glenhaven
Posts: 4,161
Quote:
Originally Posted by AndrewJ View Post
Gday Andrew
As you are a member there, just another thought re warnings.
The mount i got the earlier plot from had a lot of underlying drift as well as very large PE ( even tho it was smooth ).
In some of the runs we grabbed, the "unguided" data for DEC looked horrible, but the error was semi masked when it was guided.
I traced this back to ( very ) bad calibration data, and what appears to be the way PHD converts between sensor and sky coordinates.
I see PHD2 calculates 2 calibration angles to convert the sensor X,Y into RA/DEC.
These should always be 90deg apart ( ie X to RA and X to DEC ), but in some cases we got ( IIRC) up to 90+/-35deg difference between them.
PHD then converted the data using the 2 separate angles and as such both the displayed data and sent pulses were wrong as the RA PEC was contaminating DEC data.
Not saying thats the case here, but it is another possible cause for oddball guiding.
I have no idea why PHD2 uses 2 discrete angles, as there is no way to properly measure the DEC angle due to the PE in the RA drive????
Andrew, I think you'd do better asking Andy Glasso this one. (Yes another Andrew.) Either join the group (https://groups.google.com "open phd guiding") and send the debug and guide logs, or if you want to avoid that send me the logs and I'll submit your question.

If you are using ASCOM to do pulse guiding PHD2 is supposed to get the current RA and Dec from the mount and use the Dec to recalculate the pulse lengths as you change position.
If you are using ST-4 the recent versions can use "On camera" for guiding and have an "Aux mount" connection to get the mount position. I haven't had a change to try this yet.
Reply With Quote