PHD Guiding erratic When using SGP


Ok I am attacking my PHD Logs. The first log is Just PHD without using SGP After calibration, the cross hair jumps immediately to the guide star and begins to guide just fine.
The second log is PHD being used by SGP after calibration the cross hair does not jump back to the star. Instead PHD attempts to autoguide the star back to the cross hair and SGP times out saying guiding errorPHD2_DebugLog_2016-03-08_192233.txt (262.3 KB)PHD2_GuideLog_2016-03-08_192233.txt (8.2 KB)PHD2_GuideLog_2016-03-08_191043.txt (21.0 KB)PHD2_DebugLog_2016-03-08_191043.txt (644.6 KB)


Hi scopehead,

Thanks for posting the logs. There actually is a difference between whether guiding is started manually or automatically through SGP, and the difference has to do with PHD2’s notion of sticky lock position. When sticky lock position is enabled, PHD2 will remember the position where calibration started and move the guide star back to that position when calibration is done. When sticky lock position is not enabled, guiding will start immediately at the end of calibration wherever the star happened to end up after calibration. Sticky lock position is automatically used when calibration is initiated through an imaging app like SGP; the rationale is that the target has just been framed and it is not acceptable to allow calibration to alter the framing.

So why was this a problem in your case? Your logs show an excessive amount of backlash on your declination axis. PHD2 was unable to take up the backlash before SGP timed-out. SGP timeout problem notwithstanding, the dec backlash is going to limit your ability to guide effectively in dec at all. Here are some ideas:

  1. update to the latest version of PHD2
  2. use PHD2’s Guiding Assistant to measure your Dec backlash
  3. see if you can mechanically tune your mount to remove at least some of the backlash
  4. if you can get your backlash down to less than about 2 seconds, try enabling PHD2’s dec backlash compensation
  5. if you cannot mechanically improve your backlash, consider uni-directional dec guiding (set dec guide mode to North or South as appropriate).
  6. you really don’t want to be calibrating during your SGP sequence. Connect to your mount in PHD2 with ASCOM (or use the Aux mount ASCOM connection) so that there is no need to recalibrate at different targets. Calibrate once at the beginning of your imaging session before you start your sequence in SGP (you do not even need to calibrate from night to night unless your guide setup changes or your guide camera is rotated.)

Hope that helps,


Is there any way to disable “sticky lock position” when using sgp?

Sent from my T-Mobile 4G LTE Device


No, but if you do #6 it is a moot point because there will be no calibration during your SGP session. I highly recommend you take that approach. Calibration is really not something you want to happen unattended. The best practice is to calibrate once near declination zero. In your case with lots of dec backlash you should first remove dec backlash by moving the mount north before calibrations starts. Once you have a good calibration, you’ll want to just keep using it and avoid recalibrating, especially during an automated run with SGP.