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Bi-monthly release with minor bug fixes and improvements

Internal guider Instability with Paramount ME

  • Posts: 25
  • Thank you received: 7
I’m testing Ekos on a friend’s Paramount ME for potential use at his remote observatory. As explained in my earlier post, The ME is about 10 years old and uses the MKS 4000 control system, firmware version 2.5.19.

Configuration: RPi 4, Stellarmate OS 1.5.6 running KStars/Ekos and TheSkyX. I have run the Package Updater again just today. TheSkyX Professional is Version 10.5.0 Build 12739.

I have this running on the sky from a pier in my backyard, connected to my local network using ethernet over power line adapter. I have done a polar alignment with Pole Master and then a 60 point TPoint mount model using my MacBook laptop at the computer. I have also done a PEC curve and uploaded it to the ME (0.4 arcsec pk-pk corrected).

The telescope is a FSQ 106 EDX4 with ZWO filter wheel and ZWO ASI6200mm camera. I can get TSX to connect to the camera but it throws a time out error when trying to download an image to the Fits viewer. I cannot get the EFW to connect to TSX. I have updated the X2 plugins for the camera and filter wheel in TSX from the ZWO website on the RPi but that does not solve the problem.

So I did a polar alignment of the ME using Pole Master running on my MacBook Pro at the mount and then did a 60 point TPoint mount model to check the polar alignment. It was off several minutes so made the adjustments in Az and El on the mount as suggested in TPoint Polar Alignment Adjustment tab. Later checks with drift alignment procedure showed the PA error to be around 0.3 arc min. The mount makes 10 minute exposures with no star trailing (star eccentricity values less than 0.4).

I then tried running the internal guider. I realize I do not have an adequate guider setup. It is an old Orion 50 mm guide scope of 163 mm focal length and a Lodestar X2 CCD with 8.4 um pixels - plate scale 10.95 AS/pixel. This is bad I realize and am working to upgrade it.

I set the internal guider as follows: Exposure 3 seconds, Binning 1X1, Box size either 32 or 64 (doesn’t affect instability), Via: Paramount, Guide rate: 0.5, Dark frames: enabled. I am using the multi star algorithm (have also used Smart but same issue), but not using GPG RA guiding ( I have already done PEC correction on the ME using a curve previously generated and loaded into the mount - 2.2 arcsec peak to peak before correction and 0.4 arcsec after correction).

The guider calibrates well with seemingly no problem.

In operation the guiding goes along in a stable fashion for sometimes 10 minutes but then, for no discernible reason, starts oscillating to very large amplitudes (150 are sec peak to peak) at which point the guider quits and starts over. BTW when guiding is stable the error is never better than 1.5 AS RMS total. The unguided performance as measured by PHD2 in Guiding Assistant is 0.6- 0.7 AS RMS total. So is this a clue my guider is not measuring anything significant.

I have attached a screen grab of an error plot using Andy Glasso’s excellent phdlogview application showing typical behavior. If it would be useful, I can attach the actual guide log.

Does anyone have any suggestions about what I am doing wrong or what I can do to fix this problem? I have used the same guide scope/camera with my mount, an NEQ6, and never saw this problem.

The following user(s) said Thank You: Paul Muller
3 years 1 month ago #67011
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  • Posts: 183
  • Thank you received: 23
Here's a thought to help us debug this one. Let's trying switching the OTA/cameras around and guide with teh main OTA and use the guide scope as your imager.

Try running the whole thing again and let's see what happens. My guess is that this relates to how DirectGuide deals with commands. I ASSUME (small word, big consequcens) that you're NOT using an ST4 cable?
3 years 1 month ago #67468

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  • Posts: 25
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Paul, thanks so much for the reply! That is an excellent suggestion and as soon as this current big winter storm clears (maybe even tonight or tomorrow) I will try that. And you are right, I am NOT using an ST4 cable - via Paramount is selected.
The following user(s) said Thank You: Paul Muller
3 years 1 month ago #67480

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