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Bad periodic bumps (and crosstalk?) with new MyT

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#1 bfalls

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Posted 25 January 2020 - 06:23 PM

https://drive.google...QSx?usp=sharing

 

Here's a link to my PEC tracking log, and my PHD2 guiding log showing my issues^

 

Every minute or so I get pretty large bumps in both RA and Dec that appear to be correlated. The Dec shoots up, the Ra shoots down. Even when running guide assistant without any mount input it was pretty evident that there are large periodic bumps showing up for no reason. I'm a bit perplexed since my paramount is pretty new (5months), and I wouldn't expect to have to fiddle around so much with a 'premium' mount (I'm getting pretty frustrated at this point hahaha). 

 

 



#2 Ken Sturrock

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Posted 25 January 2020 - 06:59 PM

I had written a whole nice note with photos and arrows and a paragraph on the back of each one explaining what each one was but realized that I had failed to enter the image scale as best as I could figure it out. I'm still not sure that I did that right, but here goes:

 

First of all, I don't recall seeing you post this over on the Bisque site. If you haven't then you should as there are a lot more Paramount owners over there and that's where the Bisque staff review problems and respond to questions.

 

Second of all, I know nothing about PhD, so I'll confine my comments to the mount's tracking log. The tracking data looks fairly reasonable, I don't see any strange periodic jumps nor do I see any glaring correlation between the axes. For example, if you look at your tracking log with the autoguider graph utility:

 

Screen Shot 2020-01-25 at 16.31.11.png

 

All I see if the not-uncommon gradual drift in RA & declination, although there's a bit of a more rapid fall off in dec where it crosses the center line. The RA shows a fairly regular sinusoidal kind of curve. If this log was taken at the same 6.45 AS/pixel image scale that the PhD log indicates, that's kind of more drift that I'd expect depending on how you aligned the mount.

 

When you load it into the PEC function under the Bisque TCS utility, the cleaned & normalized RA curve looks pretty nice. Again, I don't see any strange periodic jumps:

 

Screen Shot 2020-01-25 at 16.47.08.png

 

The double hump is a little odd, but it's smooth. Now, what is the image scale of this thing? Like I said, your PhD log indicated that you had a pretty low-resolution image scale of 6.45 AS/pixel at only 120mm focal length. This is the value that I used in the graph above. Is that accurate and is it the same camera that you used to record the mount tracking log?

 

So, does that jump that you're seeing show up in the PhD log (I don't have PhD so I can't look), because I'm not seeing anything obvious in the mount's tracking log. How do the actual sub-frames that you're acquiring look? Also, if you are guiding with a finder/guider, how is it attached? Is everything tight? What is the rest of the rig? Do you have any moving mirrors or other floppiness? What's your seeing like? The guider settings aren't really aggressive are they? Have you programmed a PEC curve? Was the curve activated when you shot that tracking log?

 

Sorry, no brilliant ideas. Just questions. Maybe post all of this over on the Bisque site.

 

-Ken


Edited by Ken Sturrock, 25 January 2020 - 07:39 PM.
had to rework the graphs and further pontificate


#3 bfalls

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Posted 25 January 2020 - 07:38 PM

The tracking log itself doesn’t exhibit the issue, it was acquired with an 8300 at 480mm, I shared that more for consistency since I figured someone would ask. To view the log file all you need is PHDlogview tool from their website.

The gear used for the guide log was a qhy5liim and ZWO 30mm mini guidescope. It’s securely attached with a bolt onto a losmandy plate adapter which sits on top of my refractor.

The bumps in the PHD2 graph have a P2P error of about 8” in each axis. The PEC was active during the PHD log, the seeing was okay. Guide aggressiveness was minimal, and the bumps in both RA and Dec show even with guide output turned off. I don’t think it would make sense for dec to have sudden high amplitude jumps.

Edited by bfalls, 25 January 2020 - 07:40 PM.


#4 Ken Sturrock

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Posted 25 January 2020 - 08:08 PM

Oh, so *I* have to go download something else.....

 

OK. I got it up and running. Yeah, those spikes are pretty much bang on the MyT's worm period of 4:29.

 

Screen Shot 2020-01-25 at 17.46.30.png

 

There are some cases of unexplained cross-talk on the MyT, but other cases seem to resolve after a spring tension adjustment.

 

So, with the image scale of 2.32 AS/pixel (based on what you wrote), the mount's P-T-P PE is something like 3.3 AS:

 

Screen Shot 2020-01-25 at 18.04.16.png

 

Is that with a PEC curve uploaded and running, or is that with no PEC? I'd expect it to do better with a decent PEC curve uploaded. Strange that the spikes occur during guiding with PHD and not so obviously when "just tracking".

 

Sorry, I got nothing.... If you haven't done it, I'd still encourage you to post it on the Bisque site.



#5 bfalls

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Posted 25 January 2020 - 09:42 PM

Thank you for looking at the guide log I do appreciate it. The guide log was produced with the PEC curve running. I will also post to the bisque site. I also messaged a staff member with the same details yesterday. I don't really expect anyone on any forum to be able to diagnose what's going on.

 

I will also record a new tracking log tonight, however the CCD I previously used to capture the last curve has broken, so I have to record it at a rather sad image scale ~6". 



#6 bfalls

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Posted 25 January 2020 - 10:42 PM

Actually I got the QHY SDK working, a new guide log has been uploaded to the drive foleder taken with the qhy367. 



#7 premk19

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Posted 25 January 2020 - 11:50 PM

I noticed similar spikes in my new MyT too, though it was in RA only. I did not notice any significant crosstalk with declination (or maybe I wasn't looking closely).

 

My PE was very slightly out of spec (7.5" p-p vs guaranteed spec of 7") so SB replaced my RA worm assembly for free. I haven't had a chance to use my mount since the replacement, but I highly doubt out of spec PE was the reason for spikes in RA. I always image guided and a 7.5" p-p error over ~5 minute worm period should be easily guided out. My RA jumps were around ~4" and seemed periodic.




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