PHD Problem with Guiding
Posted 16 February 2011 - 09:22 AM
Look at the DEC error. It drifts off scale, then eventually corrects. Later on, it stayed pretty much in the middle.
My polar alignment isn't perfect, but it isn't terribly shoddy either (drift alignment 30 seconds via CCD method).
Posted 16 February 2011 - 10:20 AM
Excessive Dec backlash? Maybe needs mesh adjustment at Dec axis?
Looks like you have a sensitive guide camera. I can easily tell you are guiding M42. What kind of guide camera?
Posted 16 February 2011 - 11:34 AM
i think it was cable snag.. because after i left the laptop (which I literally had in my lap..) to wash dishes, the DEC flattened out. need to work on my brain settings though..
Posted 16 February 2011 - 12:02 PM
I see I adamsp123 guide scope info but the image scale looks about the same. Dale
Posted 16 February 2011 - 12:18 PM
the RA was not a problem, over 40 minutes (4+ worm periods) it behaved, average PE was 20 arcseconds. Except for a huge spike every worm period!
i copied the 0.03 settings from some forum blindly.. obviously not such a good idea..!
Posted 16 February 2011 - 12:32 PM
Posted 16 February 2011 - 12:54 PM
Yours seems to have taken quite a long time to flatten out, but that may be a difference in your DEC motor's guide rate.
Posted 16 February 2011 - 01:50 PM
I also agree set the min motion up, I use a 50mm finderscope and set that to about 0.5, I don't want to chase the seeing or keep sending large amounts of correction data which I believe increases the chance of unecessary oscillations in the guiding
Posted 16 February 2011 - 03:04 PM
Definitely the 0.03 px min move # is too small. Regardless of what you say about the RA not being a problem, you PHD graph says otherwise and I think you can approve. That oscillation in RA is due to too much adjustment and bouncing back and forth, likely due to the aggressive min move and 100% setting. IMHO you are making PHD do too much.
I guide at 5"/px and image at 1"/px, so I've set min move to 0.15, which is just under a 1px move for the main imaging scope scale. I set RA aggressiveness to 0.95 (or 0.9 if seeing is bad) and do 3 to 5 min exposures. This has served me fairly well and never resulted in runaway adjustments. YMMV.
One other thing I'd add, I don't know if this makes a difference, but I always try to select a guide star without any nebulosity around it if possible. This can be hard with the M42 region. I do this so the light is starlight only, and not some misshapen source that may cause an inaccurate calculation of the centroid. Again, I have no idea if this matters, but it's been my practice and served me well.