Juwei 17 guiding issues

[Eren Gencer]

Hello,

I have had guiding issues since I upgraded to a mono rig. My SWSA GTi couldn't quite handle the weight anymore and my only other option was to get something like a TeSeek or Juwei becuase of financial reasons. I have tried everything I could find about guiding with the Juwei and also tried out many combinations of variables. Guiding Assistant didn't help too much as well.

I use a Zenithstar 61 II with a Touptek filter wheel and the ATR585M. Guiding setup is ZWO 30mm f/4 and ZWO 120mm mini mono. One thing that might contribute to my bad guiding is that my guidescope doesn't ever manage to get round stars, even if I follow the manuals with backfocus etc. 

I live in a Bortle 4 zone, get good nights and use dew heaters on both scope and guidescope.

I would be very grateful if anyone could look through my log file for the last night I imaged! I bought the mount because user experience with guiding was very good from what I have read. I really hope the issues aren't mount-side..

Guide log: https://openphdguiding.org/logs/dl/PHD2_logs_a3Wt.zip

Kind Regards
E. Gencer

[Bruce Waddington]

Hi Eren.  There are a number of issues here but I don't think there's reason yet to worry about the mount.  First, you have a lot of large, spontaneous guide star excursions in the range of 3.5 - 6 arc-sec that aren't likely to be coming from the mount drive system.  Either you had terrible seeing conditions or there is unwanted movement in the guiding assembly.  This could come from something being loose or poor cable routing that is allowing a cable to tug on the assembly.  Here's an example (RA in red, Dec in green):

Notice how many of the "spikes" in guide star location are in the 3-6 arc-sec range.  Remember that in most cases, the Dec motor wasn't even running at the time so it's unlikely these are coming from the mount drive system.  Like many others, you're using a very coarse guider image scale (6.5 arc-sec/px) so these excursions can be created by a mechanical shift of just a few microns.  Next, I doubt that your guide camera is well-focused.  The stars you're getting usually have sizes of over 4 pixels which seems high for this kind of guiding setup.  Based on your comments, I suspect you may need to work harder on the focus and stability of the guiding camera.

Beyond these issues, the RA tracking of the mount has the usual periodic error problems we see with these kinds of mounts.  Here's a look at the raw tracking performance of the mount:

You can see there's a periodic error of about 40 arc-sec peak-peak with a pretty well-defined period:

You can get better control over this if you use the PPEC algorithm for RA.  Set the period length to 430 sec and un-check the box for "auto-adjust period".  Once you get these basic things sorted out, you can take another look at the results and decide if you need to further reduce your camera exposures to 1/2 second.  One final comment: at about 02:55, it looks like the mount either stopped tracking altogether or became so snarled in cabling that it couldn't track properly in RA.  This happened while pointing about an hour (15 degrees) west of the central meridian from the west side of the pier at Dec = 44 degrees.

Hope this helps,

Bruce

[Eren Gencer]

Hello Bruce,

First of all, thank you very much for taking the time to look through my logs and for your detailed help.

You're absolutely right, the mount disconnected several times, which made guiding unusable during those periods. Unfortunately, this happens quite frequently, and I haven't been able to identify the root cause yet. I've checked all the cables, eliminated any possible cable snags, and made sure everything is securely connected, but the issue still occurs. It is quite frustrating.

Following the Guiding Assistant's recommendation, I also enabled PPEC with a period length of 430 seconds, as you suggested. I have really spent quite a bit of time trying to achieve the best possible focus on my guide scope, for years. I even printed a Bahtinov mask specifically for it. Despite all that, I still can't get properly round, well-defined guide stars, they have always appeared distorted. Because of this, I suspect there may be an underlying issue with the guide scope itself. I've gotten myself a new 50 mm guide scope, which I'll be trying tonight. If the issue persists, I'll update you with the new results.

Thank you again for all your help. I really appreciate it.

Kind regards

E. Gencer

[Brian Valente]

>>> Despite all that, I still can't get properly round, well-defined guide stars,

round guidestars is not a requirement for good guiding. Many guiding setups - particularly OAGs on reflectors like SCs - have poor star eccentricity. PHD still does a good job of finding and tracking the centroids

Brian

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Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/