Resolved High Guide Errors

Discussion in 'STX and STXL' started by D Simpson, May 17, 2018.

  1. D Simpson

    D Simpson Cyanogen Customer

    Joined:
    Oct 10, 2014
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    115
    Location:
    Santa Fe, New Mexico
    Hi,
    I've been working for a while now trying to get reasonable guide numbers with my setup but the results have been very poor. I apologize for in advance for the longwinded essay I'm just trying to answer as many questions as I can so you don't have to ask them.

    So this is the problem, my guiding RMS rarely drops below 0.750as/px and generally runs much higher (1.0+ as/px) with numerous individual errors well into the +-1.0 - 2.0 and higher range.

    I'm using an STXL 11002M-FW8G/14.5" RCOS combination mounted on a Paramount MEII. The package permanently mounted on a concrete pier in a roll-off. According to TheSkyX my polar alignment is "excellent". I've got everything well balanced with a little east heavy.

    Guider Image scale is 0.66 as/px at bin 1. The main chip is 0.56as/px at bin 1.

    It's not uncommon for the errors on one axis, usually Dec, to go into a runaway mode where the errors more or less double until the guidestar is lost and guiding stops. This has happened a number of times immediately after doing a successful calibration and then trying to guide on the same star I used for the calibration.

    Watching the guidestar in the trackbox it is clearly jumping about quite a bit.

    I'm using MaxIm Pro 6.17 with ASCOM Direct - guider settings are currently the Help default MinMove 0.01 and MaxMove 2.00 with a 0.0 delay after correction. Reverse X is checked.

    Calibrations go reasonably well, nice L-shape for XY movement.

    I've tried both the Single-Star and Multi-Star options with no apparent difference in the results.

    Guidestar exposures are usually 5-6 seconds. I've tried guide exposures up to 10 seconds without any obvious improvement.

    The aggressiveness settings usually start at 5.0 for both X & Y. I've tried higher and lower with only fleeting success.

    I'm currently using a 300+ point TPoint run. SuperModel gets me to a Sky RMS of 14.1 - which seems a bit high. Pointing is fairly good. ProTrack is on and activated.

    I've used both PemPro and TheSkyX to create PEC curves. Currently, using a curve created using TheSkyX, my peak to peak is at 2.1 arcsecs.

    TheSkyX is the latest Daily Build. I've also tried guiding using TheSkyX Camera Add-on. Same wobbly results.

    Not sure what my local seeing is, probably not the best.

    This is all happening with a SkyPA of 0.0 looking east or 180 looking west. I haven't even considered adding in the rotator.

    I have the MaxIm observatory window open and the telescope connected mainly to stay on top of the Auto Flip and Auto Dec

    Guidestars are quite oval which I think is a due to a slight misalignment of the pick off camera in the FW8G.

    My goal is to set everything up with ACP but until I can get things going manually that's on the back burner.

    Any and all suggestions on where to go from here are welcome.
    Thanks,
    Dan
     
  2. Doug

    Doug Staff Member

    Joined:
    Sep 25, 2014
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    It's hard to tell "from here". Have you looked at the graphical track log?

    When I have used a Paramount in the past, I've used an Aggressiveness of 3 and an exposure time of ~1 second (or 2 if faint). The low Aggressiveness essentially creates a running average effect and results in very smooth guiding. Better IMHO to do lots of small corrections than a few bigger ones. (Some will disagree... however I did study control systems in university and it's pretty clear that extra phase lag is a very bad thing.)

    For now if you are not using ACP then you want to use Telescope not ASCOM Direct. Otherwise MaxIm DL won't be able to perform declination compensation nor handle pier flip automatically. When you use ACP then use ASCOM Direct to disable MaxIm DL's automatic compensation features.

    Oval guide stars don't matter - you are imaging off-axis and cannot expect perfect star images.

    Also please see http://www.diffractionlimited.com/help/maximdl/Autoguider_Troubleshooting.htm
     
  3. D Simpson

    D Simpson Cyanogen Customer

    Joined:
    Oct 10, 2014
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    Location:
    Santa Fe, New Mexico
    Thanks Doug, I'll start with your thoughts and recommendations. We'll see how it goes from there.
    Dan
     
  4. Mark Marfoglia

    Mark Marfoglia Cyanogen Customer

    Joined:
    Oct 19, 2014
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    Location:
    Montreal, Quebec, Canada
    Have you tried different guide stars? I have had issues where the software is tracking on one, then heads off to one side but comes back. Playing with the aggression just affects the length of the detour. It has always turned out to be another star nearby just out of the FOV.
     
  5. Colin Haig

    Colin Haig Staff Member

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    Dan, am just another customer.
    You might also post this over on the Bisque forum. Tom House is another user over there who has a lot of experience and might have an inspired suggestion.
    Any history on the mount - eg Has the mount been lubricated recently? Spring plunger screws been adjusted?
    What's the calibrate time you're using - I found I had an issue with one scope where I needed to make a bigger L.

    Have you considered disabling Y axis (DEC) motion to see what happens?
    What happens if you do an unguided long exposure (2minutes ?) any star trailing?
    Did you PEC train the mount? What's its error like? Is PEC on? (Eg you could try no PEC, no Protrack, then with PEC no Protrack, then both). Is the PEC within spec?
    Maybe ask them to assess your TPoint model.
     
  6. Doug

    Doug Staff Member

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    Colin makes a good point. Most guiding problems are mechanical in nature, not software per se. You might want to stick an eyepiece in the telescope and watch it track. Then watch it guide. Try jiggling the telescope just a little to see what happens. And of course make sure the telescope is well balanced, and that nothing is loose.

    I once had a scope on a Paramount that appeared to be working well but produced oval stars. It turned out to be a vibration issue caused by a mechanical resonance. Made some mechanical modifications how a counterweight was attached to the OTA and all was good again.
     
  7. D Simpson

    D Simpson Cyanogen Customer

    Joined:
    Oct 10, 2014
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    Location:
    Santa Fe, New Mexico
    Hi Mark,
    I don't seem to be having problems with jumping to another guidestar. From what I can tell it's the same star just jumping around too much.
    Thanks for the suggestion
    Dan
     
  8. Charles Cynamon

    Charles Cynamon Cyanogen Customer

    Joined:
    Jun 3, 2017
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    Location:
    Mount Airy, MD
    Dan

    I have a similar set up as yours, but with a Paramount MX+ and an SBIB STXL-6303e. Have you had any improvements? I am having the same issues you report.

    Chuck
     
  9. Colin Haig

    Colin Haig Staff Member

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    Chuck, please start a separate thread, and provide full information on your equipment and software, including all versions.
     

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