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Mount Performance Baseline

 

So, after a few years of on/off use of an old G8 with Gemini 1 with the AsiAir, I’m keen to up my game by moving to NINA and properly getting into guiding and PEC.?

Additionally, as my mount has steel worms and separate worm blocks, I have got replacement brass worms and single piece worm blocks. With the AsiAir and this setup with a Z61 OTA, I’m getting between 1.5 -2.2 guiding in a bottle 5/6 back garden.I also plan to clean and re-grease.

I also have an aging G11 with Ovision worm on RA which I’m yet to put into service, but will need a clean and re-grease at least.
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So, before I do anything, I’d like to get a baseline of the system performance so that I can compare it with the post upgrade performance.
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My question is, how do I get such a baseline using PHD2/NINA/something else? I’ve only used the ASIAir, so all other software is new to me. But I do at least have some concept of PHD, but no actual experience of using the full product in anger (yet!).
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Any advice/guidance on what to do gratefully received. (I have checked out Michael Herman’s approach in the documents area but not sure this is the best current approach?)
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thanks Bryn
 

Hi Bryn
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having a baseline performance for your mount is a good, systematic way of improving it, especially if your guiding is consistently in the 1.5” region, there’s improvement to be had for sure.
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For now I would suggest a couple of things.
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1- first try to learn PHD2 and use it to get a more realistic guiding performance compared to the watered down version in the AAir. Especially try to get PPEC algorithm going to try and tame your mount’s inherent PE.
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2- once you have a better understanding of the baseline guiding, get a long session in, preferably with unguided tracking (guiding assistant run for about 40 minutes) and then import the resulting guide curve into a number of software available to analyze the behavior of the mount’s moving parts. This analysis will tell you exactly where to improve. It can tell you whether the worm is the more significant cause of PE, or the oldham couplers, etc.
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For the most part step 2 can be done with your guiding sessions as well, as long as they’re long enough. If you feel like you have PHD2 setup and configured properly already, you can kill two birds in one fell swoop. Do your test guide (close to the meridian) for the required 40 minutes and then import the guidelog into PHD2 logviewer to analyze the graph.
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Share the results here and people will be more than happy to guide you (pun somewhat intended).
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Good luck
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Jonathan
 

Bryn,

Jonathan's advice on learning how to use PHD2 (and read the resulting logs) is good advice.??

However, if by "baseline" you actually meant "What can I expect from a performance standpoint using this equipment in a Bortle 5/6 environment?" then one way to do this might be to ask readers of this and similar groups to provide what they can generally achieve using similar equipment.? I exclusively use NINA/PHD2 for imaging and guiding and with my Celestron 9.25 Edge HD and G811 I can generally get just under 0.5" RMS error in both RA and DEC in my Bortle 4/5 zone, on a good night of seeing.

Note all those variables.? It might be difficult to find any direct comparison since so many factors are in play here, but those readers who have put several years of tweaking under their belts may be able to let you know what to shoot for.

Paul


On Mon, Sep 9, 2024 at 10:00?AM Jonathan via <jkaiser3000=[email protected]> wrote:
Hi Bryn
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having a baseline performance for your mount is a good, systematic way of improving it, especially if your guiding is consistently in the 1.5” region, there’s improvement to be had for sure.
?
For now I would suggest a couple of things.
?
1- first try to learn PHD2 and use it to get a more realistic guiding performance compared to the watered down version in the AAir. Especially try to get PPEC algorithm going to try and tame your mount’s inherent PE.
?
2- once you have a better understanding of the baseline guiding, get a long session in, preferably with unguided tracking (guiding assistant run for about 40 minutes) and then import the resulting guide curve into a number of software available to analyze the behavior of the mount’s moving parts. This analysis will tell you exactly where to improve. It can tell you whether the worm is the more significant cause of PE, or the oldham couplers, etc.
?
For the most part step 2 can be done with your guiding sessions as well, as long as they’re long enough. If you feel like you have PHD2 setup and configured properly already, you can kill two birds in one fell swoop. Do your test guide (close to the meridian) for the required 40 minutes and then import the guidelog into PHD2 logviewer to analyze the graph.
?
Share the results here and people will be more than happy to guide you (pun somewhat intended).
?
Good luck
?
Jonathan
 

 

Thanks Paul. By baseline I was really looking at how is my mount performing currently so that I can determine what effects the upgrades have.
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However, your point regarding what can I expect from it I’ve never actually thought too much about. Sub 1 would be good I guess as I extend my focal lengths?
 

Thanks Jonathan, I’m hoping to start the process in a day or two as currently in the process of reconfiguring scopes away from the ASIAir setup. I eventually want to go to a dual Z61 setup once I’ve sorted the mount and got familiar with pHD2 and NINA.
 

Hey Bryn
With a wide field scope like the Z61 you should be able to achieve sub 1 arc-sec at the very least. Once your worm is adjusted I imagine you could achieve ~0.75 (maybe better?… seeing dependent).
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Personally my G11G was guiding at 0.75-1.1 arc-sec without too much trouble once I fully understood the worm adjustment procedure and balanced the mount well. That was for the first 18months of ownership. At that point I had a better understanding of the adjustment process and managed to fine tune it a little more with good PEC and I’m down to 0.5-0.6 arc-sec. This is with the default PHD2 settings the whole time.?

I’d aim for sub 1 arc-sec for now. With time and practice, it will come down.?
 

As for how to get a baseline, set up the PHD2 profile, and follow Michael Herman’s steps here in the attached file. This is one he gave me about a month ago. I’m not sure if this was the process you followed/referred to below but it worked well for me.?

Periodic Error Measurement in Telescope Mounts by Michael Herman December 9 2022 v2.pdf
Periodic Error Measurement in Telescope Mounts by Michael Herman December 9 2022 v2.pdf

 

So, I have had my first attempt at trying to get a baseline. I followed the guidance above and produced the logs in the attached file over about 50 mins on a GM 8, with Zenithstar 61 at 360mm focal length.
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Even despite the explanations given in Michael's documentation, I have no idea what I'm looking at! Whatever it is, to me at least, it doesn't look good?
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If anyone could give me any pointers, that would be great!
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GM8, original steel worms and 2 piece worm blocks probably needs some TLC which is why I trying to get a baseline (I have new grease, brass worms and one piece work=m blocks for each axis to go in) before I implement upgrades.
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Many thanks
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Bryn

PHD2_GM8_PETrack_GuideLog_2024-09-16_225006_Zenithstar61_1600MMPro.txt
PHD2_GM8_PETrack_GuideLog_2024-09-16_225006_Zenithstar61_1600MMPro.txt

 

Bryn,
Nice work. This is not a simple process to navigate but I think you are doing fine. Toward the bottom of Michael Herman's instructions he goes into how to interpret your recorded guide logs. I went ahead and loaded yours into PECprep and took a look... your raw guide log showed a little polar alignment error, which is why the DEC and RA lines sloped up. While you want that to be as accurate as possible, as far as I understand it, that is not a show stopper (my feelings won't be hurt if someone needs to correct me).
I used the focal length you gave (360mm) and made an assumption on the pixel size since you labeled the file ASI1600. The screen capture above is what I saw after I clicked "Auto Filter" at the bottom. This measured a "baseline" peak periodic error of your mount at +9.75/-9.57 arcsecs, while the average periodic error was +3.0/-3.64 arcsecs and the MaxRate was 0.36 arcsec per second... sidereal rate is 15.041 arcsec per second so this should be well within the capabilities PHD2. The next tab show what a generated PEC curve might look like if you loaded it into your mount. This is a little superfluous at this point, since we are just talking about recording a starting point, but it does give us some data, there are some large swings in your curve besides from your worm gear and it does look like your worm gear adjustments could be tweaked. I'm a newer mount owner (G11 with Spring Loaded worm and tucked motors) so the other guys out there with single piece worm blocks may have better experience conveying worm adjustment techniques.
Finally if we look at the frequency spectrum tab I see two large spikes. One is your worm drive and one is about 1/3 of your worm period. This may be an oldham coupler that needs to be adjusted? I'm not too familiar with the single piece worm, sorry... but it does seem like worm adjustment could give you the most bang for your buck.
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as far as comparison goes, I'll show you my own mount after I tweaked the oldham coupler, cleaned and regreased my worm/ring gear/needle bearings, and refined the spring loaded worm tension:
Period error got down to about plus or minus 1.5 arcsec with average error plus or minus half an arcsec.
PEC can cut that in half, which is pretty much what I see in practice, getting me to seeing-limited guiding. If the seeing is average, I can guide within 0.5 arcsec... if I get blips of excellent seeing it may drop to 0.35 arcsec for a little bit. Poor seeing is up near 0.8 arcsec or greater. Various blips on the curve are visible on the screenshot below. You can see that PECprep gives a little more detail for the G11 setting than it does for your G8 setting. That huge mountain to the right of the curve is from polar alignment error... it is a super long period error that you can pretty much ignore.
Basically I shared my PECPrep results so that you can see what is possible and see that even with small periodic error left over, you are still going to have some spikes on the graph.?
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Hopefully it gives you an idea of where to go from here. Try following the worm adjustment instructions until you can reduce that worm period and 3rd harmonic peak. From what I've heard from other folks here and there, your starting point is really not too bad, but there is room for improvement. There are of course mechanical upgrades you can accomplish, but I would encourage you first to try and maximize what you have first. When you accomplish that, if you still want to upgrade to a precision brass/ spring loaded worm you will have a newer and better baseline to compare that to.

Hope that helps Bryn, and I hope that someone out there with a one piece worm block can offer up some sagely adjustment advice.
Good luck and clear skies,
Ryan
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I re-read that you already have the brass worms in hand. Curious what a measurement with those in would look like. I'm curious how much improvement others have seen as they transition from steel worms to brass. I've only had the brass ones.?
 

Ryan,
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Thanks so much for your time looking at this and your observations, it definitely gives me a starting point of what to look at. My current plan is to adjust what I can with the mount as it is (steel worms, original worm blocks, existing grease etc) to see where I can get to. Hopefully this will then give me a good (and improved) baseline before I dismantle, re-grease, install new worms and one piece worm blocks with Belleville washers. I’ll also look into whether replacing the oldham couplers is feasible too as getting them in the UK might be tricky? Hopefully after all that, and correctly adjusting everything, there will be an improvement?
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Then it’s similar again with my ageing G11 with an Ovision RA worm. The difference this time being that I don’t currently have any upgrade parts, so it would be adjustment and re-grease only.
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I forgot to mention that I polar aligned with a polemaster (first ever time doing it), so will look at that again and also confirm alignment with NINA 3 star PA. (Also never done before). I might also try another first of drift alignment just to get the best baseline I can! At some point, I might actually get some imaging done!

Thanks again and any more advice welcome.
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Bryn
 

That seems like a great plan to me.
I also use the Polemaster most consistently. I also have used the NINA 3-point PA (TPA) and the PHD2 Drift Align. To me the Polemaster is the most consistent and the fastest. I have found that If I use any of those methods and I require a large initial adjustment to dial in the alignment, I will use the first iteration of the alignment to get it pretty close and then restart the alignment again from scratch. This tends to give me more accurate and more repeatable results. If you use the NINA TPA I would read through the documentation for recommendations. Personally I find the pointing declination about 35-50 degrees from Polaris works most consistently for me but your mileage may vary.
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If I leave my mount set up on the back porch, I find I generally do not have to re-align each night, but rather, I will cold start the mount at CWD, open PHD2 through NINA, use calibration assistant (Tools > Calibration Assistant) to slew to the meridian at 0 declination, and then I cancel the calibration (I reuse mine) and run guiding assistant instead (Tools > Guiding Assistant) for 2-5 minutes.

I find this functions as a "check" of my unguided performance for the night, it gives me a easily understandable reading of my polar alignment error, and gives recommendations for my PHD2 sensitivity based on the seeing. I like to see "less than an arc second" but I accept anything up to about 6 arc seconds with my 1300mm focal length. If it is more than that I reattempt polar alignment.
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I will also add that my recommendation is that while you should attempt to refine your polar alignment error, I'm not personally convinced that you should trust it to the Nth degree; that is, I wouldn't lose any sleep over it as the software will tell you your "error" with the utmost confidence, yet if you run it immediately again afterwards without changing anything you will most likely get a slightly different result. We are talking about fractions of a hair's width in accuracy combined with hand-adjustable parts and mechanical flex which can not totally be eliminated. By doing the best you can, within reason, and being consistent, you will reduce the effect of polar alignment error below the noise floor of your imaging session. Some slight polar alignment error can actually help offset declination backlash. PHD2 is pretty incredible.
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I like to say "measure with a micrometer, mark it with chalk, cut it with an ax."

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