Guiding Drift After Dither PHD2

[PottyMonster]

Hi All, I'm having an issue with PHD2 guiding where after (what seems to be) every other dither the guiding drifts in declination. For some reason it seems to be after a "heavy" dither and seems to be pretty consistant. I've attached 3 screen shots from a recent night, two showing the problem and one showing a good "dither recovery".

Any advice? I've had this problem for a while and just ignored it as it does eventually sort itself out, but it is wasting time every evening , and with shorter nights every second counts!

[Tomatobro]

If only when dither North (the last one looks to be ok) then backlash would be the first thing I would look at.  If the mount is always correcting north during guiding then its just taking  while for the backlash to be taken out.

 

[Vroobel]

I experienced the same with my CGX, so have to check the backlash too. The funny thing is that it doesn't affect stars shape, they are OK as long as trend lines are horizontal. 

[Clarkey]

Run the guiding assistant and it will measure your backlash. It looks quite bad. Also, it will help with other settings.

[michael8554]

1.  "every other dither the guiding drifts in declination."

That could be due to PA error - did  you do a Guide Assistant run, that will report the PA ?

But may also be due to Dec Backlash

If Dec was balanced south heavy it will tend to be pulled to that end of the Backlash.

Maybe some Stiction too, as Dec was not reacting to the corrections for a long time.

The tiny 1 pixel Dither to the south was easy to correct, the bigger north dithers were not.

2.  Are 1 to 3 pixel Dithers worth doing ?

3.  Set your Y-axis to arcsecs.

4.  3 sec exposures are too slow for MultiStar guiding, try 1 or 2 secs.

5.  HFD at 5.30 is large, is this Off Axis Guiding ?

Some clue to your setup would help.

Michael