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  1. #1
    Join Date
    May 2006
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    138

    Default Still having Guiding Problems - Mount tracking

    Searched but did not see the answer. Maxim 6.21/ACP 8.2/SBIG STL6303E/Gemini rotating focuser/AP 1600 GTO/Planewave 17/ASCOM direct guiding.

    In the guider tab, on the left side "auto scope dec" on or off? "Auto pier flip" and "pier flip" on or off? In ACP, "use declination compensation" yes or no? It is my understanding that ACP and Maxim will have a conflict if these are not set correctly. Not quite sure what might have a conflict with what and the settings might be.

    Have the guide>settings>advanced have min move of .02, max of .15. It has been suggested that I set the "delay after correction" to a long period like 5"-10", and run a guide exposure of a short period, 1"-3". This make sense?

    Thanks...Mike

  2. #2
    Join Date
    Oct 2005
    Location
    Mesa, AZ
    Posts
    33,158

    Default

    Hi Mike -- Get your guiding working in MaxIm stand-alone first, then... Those guiding settings apply when you are using MaxIm's Observatory Control. Do not connect the Telescope (or anything else, really) in MaxIm's Observatory Control tab. Let ACP take care of it all. If you need to guide your mount with software (pulse guiding etc) then in the guider setup tab select ASCOM Direct for the Control Via. This is all covered in the ACP Help Guiding section.



    Last edited by Bob Denny; Oct 26, 2020 at 13:04. Reason: spelling
    -- Bob

  3. #3
    Join Date
    May 2006
    Posts
    138

    Default

    Thanks Bob, guiding is setup but was unclear about three specific Maxim settings: auto scope dec, auto pier flip and pier flip. So keep all of these OFF?

    Also, ACP's declination compensation, on or off? People have varied opinions about its usefulness and some have offered it can add inaccuracies.

    Thanks, Mike

  4. #4
    Join Date
    Nov 2015
    Location
    Christchurch, Dorset, United Kingdom
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    347

    Default ACP - MaxIm guide settings.

    Quote Originally Posted by Mike Shade View Post
    So keep all of these OFF?

    Also, ACP's declination compensation, on or off? People have varied opinions about its usefulness and some have offered it can add inaccuracies.

    Thanks, Mike
    Hello Mike.

    Looking back over your post history it seems you have been chasing these same guiding questions over several separate posts for some time but never resolving them?

    In MaxIm, guide settings, Auto scope dec, Auto pier flip and Pier flip should all be disabled when using ACP, you only activate these settings if necessary with particular mounts when using MaxIm as standalone in conjunction with MaxIm's Observatory Control module.

    Declination Compensation in ACP guide setup is useful in some circumstances.

    If you have a good quality mount that includes permanent PEC then with declination compensation enabled you may find the mount suffers RA oscillation when pointing to targets close to the pole in poor seeing conditions as the mount starts chasing the seeing and overcorrecting.

    For a poor quality mount with significant uncorrected periodic error then declination compensation may improve guiding when the target is close to the pole but there is no hard and fast rule here as there are so many variables at play.

    Note though that the function of declination compensation is not consistent across the different guide modes in MaxIm and for ASCOM direct guiding with mounts such as a Paramount for example the guide correction signal from MaxIm to the mount is sent as a defined arc-second mini-slew, for want of a better term, and declination compensation is irrelevant in this mode but when using on-camera guide relays and a cable from the ST4 guide port on a camera to the ST4 guide port on the mount then the guide signal is sent as a variable time duration pulse. When using the on-camera relays method in MaxIm then declination compensation is relevant and has a big effect approaching the pole.

    It is really important to experiment with the various guide settings in MaxIm alone before integrating with ACP, IOW, MaxIm must be able to produce excellent guiding at all DEC angles before handing over control to ACP and with MaxIm it is my experience that you may need to spend a couple of nights on this to fine tune the settings.

    For my own Paramount MX I found that guiding on targets close to the pole suffer from RA oscillation if DEC compensation is enabled in ACP and for my mount/OTA combination guiding is optimal when DEC compensation is disabled in ACP.

    Your experiments should reveal which is best for your setup.

    If you have not already read it, there is a document by Jim McMillan included with ACP Help that explains the intricacies of setting up auto guiding, you will find a shortcut to Jim's document in the "Auto Guiding Your Mount" tab of ACP's built-in help library.

    William.
    Last edited by William Bristow; Oct 25, 2020 at 21:02. Reason: Added distinction between ASCOM direct and relay guiding

  5. #5
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    May 2006
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    138

    Default

    Thanks William. Yes, there have been issues with the RA axis for a bit. It seems that I would get slight elongation in RA. System is AP1600GTO/Planewave 17/SBIG STL6303/Optec Gemini. I have trained innumerable PEC curves with this mount and in looking at the data, curves look good. Results are different though. Mount corrected in RA quite a bit Last night, trained a PEC curve near zenith, seven worm cycles. A 382" (worm period) unguided image near zenith looked very good, round stars across the field. As the telescope tracked further west, the stars became more out of round, going from slightly off to significantly degraded. Everything on the system is "tight", there is no mirror flop, fasteners are tight and so on. Pointed south, even worse. In desperation tightened clutches on mount more snug, wondering if it was slipping. This made it even worse, getting double "dumbbell" stars. Same thing higher up, 65 degrees elevation. Backed off clutches, going to finger tight. Images improved significantly, stars being slightly off instead of a frame of doubles. I'm not sure what is happening, suspect that the clutches were overly tight and it was binding in RA, not tracking smoothly. A PEC curve wouldn't capture this as it seems to depend on RA loading. As a note this is a "first generation" 1600GTO and the documentation offers that the clutches be hand tight and then another 1/3 turn with a wrench for heavy loads. I have run it this way for years but my results last night suggest that this may be causing issues running them this tight. There was a significant difference between the tight clutch image and the backed off image, shot same location, just backed off the clutches. I suspect that if I run a new "clean" PEC curve that might fix the problem. It might be that guiding was trying to compensate for a binding RA axis. Will report results of my experiments. Thanks again, Mike

  6. #6
    Join Date
    Nov 2015
    Location
    Christchurch, Dorset, United Kingdom
    Posts
    347

    Default Choosing the right target star for accurate PE data collection.

    Mike.

    I have no experience with AP1600 mounts per se but in general for German mounts PE calibration is carried out using a star at, or as close to DEC zero, and as near to the immediate western side of the meridian as possible, never near the zenith.

    At DEC zero and close to the meridian any deviations of the worm profile cause the target star being used to acquire the PE curve to move the greatest distance across the camera sensor so the resulting S/N ratio of worm error is high allowing a true measurement of PE to be captured and an accurate PE curve to be calculated.

    As the target star used for PE calibration assumes higher DEC angles closer to the pole then the apparent motion of the target star at the camera sensor for a given worm error becomes much smaller and the S/N ratio of worm error falls, leading to greater uncertainty over the real worm profile for PEC curve generation.

    Your description of a guiding problem that varies with different pointing angles sounds more likely to be poor worm to gear contact pressure, dry lubrication of the gears, or some other mechanical defect and nothing to do with PE whose mechanical effect is a constant wherever the mount is pointing, we only choose to measure PE at DEC zero and close to the meridian because that is where PE has the greatest “apparent” error.

    Once PE is measured and a correction curve has been applied then the effect of that curve is proportional to DEC angle, it’s corrective effect at the camera sensor, or the eyepiece, is exactly proportional to whatever DEC angle the mount points.

    To put it another way, once PE is measured accurately and a PE correction curve loaded to the mount then PE becomes invisible and has no influence over guide settings or guide operations wherever the mount is pointing.

    HTH

    William.
    Last edited by William Bristow; Oct 25, 2020 at 21:04.

  7. #7
    Join Date
    May 2006
    Posts
    138

    Default

    Thanks, the problem I was having, at least last night, was rectified by loosening the clutches on the mount. I shot an unguided image for one worm period, dumbbell shaped stars, loosened the clutches significantly, stars almost but not quite round, a significant improvement. It was the same field shot just a few minutes after the bad frame image. Images attached. The only thing between these two images was loosening the clutches. I have sent an e-mail to AP about this as the clutches were adjusted according to their specs. If clear tonight, will do some additional testing. Thanks again, Mike


    PEC CLUTCH TIGHT.jpgPEC HAND TIGHT.jpg

  8. #8

    Default

    Look familiar? I had exactly the same symptoms, AP1600 mount with doubled stars that would be gone the next exposure. I'm not saying this is the same problem you are experiencing but the resemblance is too coincidental. I finally diagnosed my problem to two air conditioners within 45 feet of the observatory. It is located in a cluster of buildings, two of which are air conditioned. While running, there is enough vibration through the sandy Florida panhandle soil into the 1 cubic yard concrete footing then into the pier to cause the 'double-taped' stars. I can tell which air conditioner is on by the angle of the parings. I am investigating wi-fi controlled thermostats since I invariably forget to get the air conditioners turned off manually. You just might want to investigate sources other than the mount.
    Attached Images Attached Images

  9. #9
    Join Date
    Nov 2008
    Location
    me: Albuquerque scope: Mayhill, NM
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    1,079

    Default

    Sounds like a job for anti-vibration mounts, for the AC compressors. Grainger and McMaster-Carr (and probably others) sell them in all sizes.
    measuring space rock rotation rates, live from Albuquerque NM

  10. #10
    Join Date
    Oct 2005
    Location
    Mesa, AZ
    Posts
    33,158

    Default

    William -- Thanks for taking the time to note that Mike has been having guiding problems in other threads here. I should make a habit of doing that myself :-) I really appreciate your taking the time to do so!
    -- Bob

 

 

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