Guiding

[Fran Doherty]

Like everybody here, I am having issues with my guiding performance. My RA and DEC RMS values are generally greater than 1.0 and I think this can be improved. Hopefully somebody can provide some insight. My equipment and imaging environment is described below.

I am using an Esprit100 which weighs 24 pounds with imaging train consisting of field flattener, rotator, OAG with ASI290MM mini guide camera (2.9 um pixels) and ASI2600MM main camera (3.76 um pixels).

My mount is strain-wave drive Pegasus Astro NYX-101 sitting on a carbon fiber tripod with legs retracted. The tripod is recommended to carry less than 33 pounds for imaging by Pegasus. They have tested this exact same combination of scope (theirs 29 pounds) and tripod with marketable results.

I have no cables that come close to touching either my guide camera or main imaging camera.

My guide camera focus is decent, HFR values between 3-4. I am not binning, although I have set up a new profile and I will try binning next time.

I image only at home from my driveway. Because I live surrounded by trees, I have no choice in location.

I understand re the large RA harmonics with a strain wave drive relative to a standard EQ mount with worm gears. I know tracking won’t ever be modeled as precisely as my previous CEM40 but was expecting a bit better performance. I use the PPEC algorithm. Pegasus claims better guiding than I am getting.

I have uploaded two logs from consecutive nights. Polar alignment appears to be good these nights. I have also uploaded a log with my latest calibration. Getting a good calibration with this mount is frustrating. I just keep trying until the mount is in a stable RA position and eventually it succeeds.

I am having settling issues being reported from NINA. I dither every 3rd image, 13 pixels (computed to dither 10 pixels), minimum settle time 10 s, maximum 40\50 seconds (tried 40 one night and 50 next.) , pixel tolerance 1.5 pixels. Settling seems to start out OK and then begins failing. This issue would be nice to solve, but I don’t think it is a real problem.

I did have one weird period at the end of the first section of my 2024-7-19 log where all of a sudden my DEC and RA excursions are almost a mirror image of each other. It “fixes” itself, but am curious what caused this?

So in general, I guess I am looking for a general check-up on my guiding and any suggestions for improvement.

Link below to logs:

https://openphdguiding.org/logs/dl/PHD2_logs_fVhA.zip

Many thanks in advance,

Fran Doherty

[Bruce Waddington]

Hi Fran.  I would say your mount has pretty serious problems with RA tracking, among the worst I've ever seen.  Here's what the tracking looks like without guiding:

And here's the major contributor to the error, an excursion with a period of about 430 seconds:

This is why you're having such challenges with calibration.  Depending on where you are in the phase of the tracking error - east or west - the west-calibration is going to see tracking that is either "too fast" or "too slow".  In RA, the west calibration for your setup takes about 20 seconds, during which time there will be about 2 arc-sec of tracking error.  During the Dec calibration, the RA axis will continue to wander around like this and you will then get these randomly large measures of orthogonality error.

I think you need to go back to back to Pegasus with this data and ask for the mount to be repaired or replaced.  It would be hard to imagine this sort of performance falls within spec.  In other areas, you shouldn't be using calibrations that encounter numerous lost-star errors.  You should also be running the guiding assistant to get recommended adjustments to the Min-Move values for RA and Dec. 

Good luck,

Bruce

[Fran Doherty]

Hi Bruce, thank you very much for looking at my logs. The RA period of 430 seconds is a feature of these mounts; that is the value that they suggest to populate the period length in the PPEC algorithm. They say that after two worm periods the PPEC algorithm should be able to handle this. I do see improvement in the star shape by my fourth 5 minute sub, but think it should be much better. Knowing this, do you still feel that my mount should be repaired/replaced by Pegasus?

Thanks,

Fran

[bw_m...@earthlink.net]

It’s just my personal opinion, but I think any mount that has a peak-peak periodic error of 90-100 arc-sec is a poor piece of gear.  These guys shouldn’t be talking to you in terms of generalities, they should know how their mounts should perform and have a standard for what’s acceptable.  For the other strain wave mounts that I’ve seen data for, the error is nowhere near this large.

 

From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> On Behalf Of Fran Doherty
Sent: Sunday, July 21, 2024 12:48 PM
To: Open PHD Guiding <open-phd...@googlegroups.com>
Subject: [open-phd-guiding] Re: Guiding

 

Hi Bruce, thank you very much for looking at my logs. The RA period of 430 seconds is a feature of these mounts; that is the value that they suggest to populate the period length in the PPEC algorithm. They say that after two worm periods the PPEC algorithm should be able to handle this. I do see improvement in the star shape by my fourth 5 minute sub, but think it should be much better. Knowing this, do you still feel that my mount should be repaired/replaced by Pegasus?

 

Thanks,

Fran

On Sunday, July 21, 2024 at 1:52:36 PM UTC-5 bw_m...@earthlink.net wrote:

Hi Fran.  I would say your mount has pretty serious problems with RA tracking, among the worst I've ever seen.  Here's what the tracking looks like without guiding:

 

 

And here's the major contributor to the error, an excursion with a period of about 430 seconds:

 

 

This is why you're having such challenges with calibration.  Depending on where you are in the phase of the tracking error - east or west - the west-calibration is going to see tracking that is either "too fast" or "too slow".  In RA, the west calibration for your setup takes about 20 seconds, during which time there will be about 2 arc-sec of tracking error.  During the Dec calibration, the RA axis will continue to wander around like this and you will then get these randomly large measures of orthogonality error.

 

I think you need to go back to back to Pegasus with this data and ask for the mount to be repaired or replaced.  It would be hard to imagine this sort of performance falls within spec.  In other areas, you shouldn't be using calibrations that encounter numerous lost-star errors.  You should also be running the guiding assistant to get recommended adjustments to the Min-Move values for RA and Dec. 

 

Good luck,

Bruce

 

On Sunday, July 21, 2024 at 9:14:20 AM UTC-7 Fran Doherty wrote:

Like everybody here, I am having issues with my guiding performance. My RA and DEC RMS values are generally greater than 1.0 and I think this can be improved. Hopefully somebody can provide some insight. My equipment and imaging environment is described below.

I am using an Esprit100 which weighs 24 pounds with imaging train consisting of field flattener, rotator, OAG with ASI290MM mini guide camera (2.9 um pixels) and ASI2600MM main camera (3.76 um pixels).

My mount is strain-wave drive Pegasus Astro NYX-101 sitting on a carbon fiber tripod with legs retracted. The tripod is recommended to carry less than 33 pounds for imaging by Pegasus. They have tested this exact same combination of scope (theirs 29 pounds) and tripod with marketable results.

I have no cables that come close to touching either my guide camera or main imaging camera.

My guide camera focus is decent, HFR values between 3-4. I am not binning, although I have set up a new profile and I will try binning next time.

I image only at home from my driveway. Because I live surrounded by trees, I have no choice in location.

I understand re the large RA harmonics with a strain wave drive relative to a standard EQ mount with worm gears. I know tracking won’t ever be modeled as precisely as my previous CEM40 but was expecting a bit better performance. I use the PPEC algorithm. Pegasus claims better guiding than I am getting.

I have uploaded two logs from consecutive nights. Polar alignment appears to be good these nights. I have also uploaded a log with my latest calibration. Getting a good calibration with this mount is frustrating. I just keep trying until the mount is in a stable RA position and eventually it succeeds.

I am having settling issues being reported from NINA. I dither every 3rd image, 13 pixels (computed to dither 10 pixels), minimum settle time 10 s, maximum 40\50 seconds (tried 40 one night and 50 next.) , pixel tolerance 1.5 pixels. Settling seems to start out OK and then begins failing. This issue would be nice to solve, but I don’t think it is a real problem.

I did have one weird period at the end of the first section of my 2024-7-19 log where all of a sudden my DEC and RA excursions are almost a mirror image of each other. It “fixes” itself, but am curious what caused this?

So in general, I guess I am looking for a general check-up on my guiding and any suggestions for improvement.

 

Link below to logs:

 

https://openphdguiding.org/logs/dl/PHD2_logs_fVhA.zip

 

 

Many thanks in advance,

Fran Doherty

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[Brian Valente]

Fran

>>> The RA period of 430 seconds is a feature of these mounts; that is the value that they suggest to populate the period length in the PPEC algorithm.

the issue is not the period length, it's the amplitude of the error. You can share the information with them below and ask if a +/- 50" is considered within factory spec.

Brian

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[Bruce Waddington]

Coincidentally, someone else posted shortly after you did and included a link from Pegasus that seems to define what their expectations are:

https://pegasusastro.com/nyx-101-guiding-recommendations/

The peak-peak tracking error they're talking about is much more in line with what we see from other strain-wave mounts.

Bruce

[Fran Doherty]

Bruce, yes, I am very familiar with this document.  I follow these recommendations and what I sent are the results. I can not duplicate their results. 

[Bruce Waddington]

I'm not sure you're seeing my point.  Here's their quote:

"The cycle concludes with another spike in periodic error during the final two minutes. In totality, this periodic cycle spans 7.16 minutes or 430 seconds. Our gear systems exhibit a measured periodic error of ±20 arcseconds or less, underscoring their reliability and precision"

They're talking about a peak-peak error of 40 arc-sec - yours is 90 arc-sec. 

[Fran Doherty]

Bruce, sorry, yes, I do understand. Thanks so much for analyzing this for me. It is no wonder I have struggled so much, basically never had a chance! I will contact Pegasus and see what they say. They have always been responsible. The company was founded by imagers and they provide a lot of the support themselves. 

[Fran Doherty]

Hi Bruce, thank you very much for looking. The excursion period of 430 seconds is common to these mounts. That is exactly the value they publish as the starting value for the PPEC period. Knowing this, does this change your opinion at all re my mount needing repair/replacement? 

On Jul 21, 2024, at 1:52 PM, Bruce Waddington <bw_m...@earthlink.net> wrote:

Hi Fran.  I would say your mount has pretty serious problems with RA tracking, among the worst I've ever seen.  Here's what the tracking looks like without guiding:

<RA_TrackingError.jpg>

And here's the major contributor to the error, an excursion with a period of about 430 seconds:

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<RA_TrackingError.jpg><RA_FFT.jpg>

[Brian Valente]

Hi Fran

>>> The excursion period of 430 seconds is common to these mounts.

the period length is not the issue, it's the amplitude of the error. 

It's this part where your system isn't matching their spec:

Our gear systems exhibit a measured periodic error of ±20 arcseconds or less,

As Bruce said, They're talking about a peak-peak error of ±20 arcseconds or less - yours is ±45 arcseconds

Brian

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/7598F87F-16E6-403B-9D23-BDB5830E43F3%40gmail.com.

[Fran Doherty]

Hi,

I am planning to get some unguided data in order to supplement my case with my NYX-101 mount. I have sent them all of the information I provided here, but at this point in time, Pegasus Astro refuses to consider that my mount may have mechanical issues and are insistent that it is a guiding parameter and star mass/seeing issue. Their persistent and only suggestion is for me to lower my camera gain, increase my max ADU saturation to 65535, and remove my 2x2 noise reduction setting. 

Anyway, my question regards how much unguided data I should acquire? My gear period is 430 seconds.

Many thanks again,

Fran

[Brian Valente]

Fran

I suggest you gather at least 30 min of unguided data using the guiding assistant

If you can share that result here we would be interested in it as well. Unguided data removes any "phd settings" that may contribute to this

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/71c9b526-3825-47af-851c-79bd83eccbc1n%40googlegroups.com.

[Fran Doherty]

Thanks for your help Brian. I will definitely do so. 

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i5Tn-zaSFu9i42wOm3zK9BWwwsfk9C4yBTTeUt8u%2Bmc-g%40mail.gmail.com.

[Bruce Waddington]

It sounds like they don't understand the graph you (presumably) sent them.  It shows the tracking behavior with the guide commands removed.  Running the Guiding Assistant for 30 minutes is a good idea because it is a completely clean, unambiguous test - but you should expect to see something that looks much like the graph we sent you.  The other suggestions are fairly ridiculous, they sound like front-line support checklist items when someone is complaining about a guiding problem which is not what you have.  To take just one example, you're running your camera in 8-bit mode, why would you change your saturation level to a 16-bit value? 

Good luck with them,

Bruce

[Fran Doherty]

Hi Bruce,

Thanks, and I totally agree, even I understand that much re this issue. I did indeed send that graph and all of the logs I sent you, even gave them a link to this thread. The suggestion I mentioned was the first thing they told me, and even after I reiterated what I am seeing, got the same suggestion. I went around their support guy and sent the support thread to who I believe is one of the company founders who sometimes answers support. He is almost always helpful, but I know he is busy and I don't think he actually looked at anything I sent initially, just assumed I was making guide parameter mistakes (i.e image scale etc). After a couple of tries with him, he gave me the below response::

The guiding is indeed bad. The mount should guide close to 0.5-0.6 arcseconds. However I am certain that this is not a mechanical failure. We deal with the similar issue multiple times and it always has to do with PHD settings and image scale of guider. A wrong image scale of your guiding camera or bad seeing (I can see that your star is not steady) obscures the PE reported graphs and gives the assumption that you. have very high PE drift, which is not in this case.

So, at this point I don't really feel I have much recourse but to try their guiding suggestion and sent them the latest logs. After they receive and hopefully look at the unguided data, I will know more where I stand with them. 

Again, many thanks for whatt you guys do for our comminity.

Fran

[Brian Valente]

Fran

You should double-check and confirm your image scale is correct (i'm not suggesting it isn't, but you will need to prove to them the image scale is correct. have your focal length and camera model/pixel size included in your report to show how the image scale is calculated)

the unguided results speak for themselves, they do not involve any guide pulses, so it can't come from that. We can help you with conveying what the data says

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/14c558f5-7093-4f4b-83fb-48ac2e3788e5n%40googlegroups.com.

[Fran Doherty]

Bruce, 

I did that Bruce, it is correct. Sent them all my PhD advanced parameter panels. Those suggestions were their answer. I think my guiding is technically ok, just is no way to correct this magnitude of error. I have also posted on cloudy nights re this issue, in reply to another NYX-101 user that is seeing the same peak to peak issues I am. I wanted him to know he not the only one with this issue.
 Fran

[Brian Valente]

(This is Brian, but close enough ;) )

I agree with Bruce they may not be paying attention to your details and giving a standard answer

Doing the unguided run should put any questions they have to rest

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/94825a9d-7371-40ea-bd08-b3453d0c44d0n%40googlegroups.com.

[Fran Doherty]

Sorry Brian!

[Fran Doherty]

Hi Bruce and Brian,

I captured some unguided data last night. Unfortunately only was able to obtain about 26 minutes (was aiming to get more) due to my scope drifting inline with a large tree. I can redo, starting scope in a different location, but would not be for a week or so. 

https://openphdguiding.org/logs/dl/PHD2_logs_WH6e.zip

It appears to me to show more of the same, but at least I can hopefully get Pegasus to realize that my guiding parameters have not caused this.

Let me know what you think.

As always, many thanks for your help.

Fran

[Brian Valente]

It does show the behavior, but imo i think you'll need to redo this

The problem is you didn't calibrate at the start to demonstrate a good calibration, and the data looks suspect. 

In your unguided results you should have a flat Dec line (red) and instead it's showing some bleed from the RA. 

It's possible the error in RA is so high that it this can't be avoided, but it's worth another shot at redoing this data.   

25 min is plenty to demonstrate the behavior

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/ee0e9e74-ff1c-4b8e-8986-8d226930036fn%40googlegroups.com.

[Brian Valente]

And just to be clear, you should have a guidelog that shows your calibration as part of your deliverable to them

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/ee0e9e74-ff1c-4b8e-8986-8d226930036fn%40googlegroups.com.

[Fran Doherty]

Hi Brian,

Thanks for looking at this and your analysis. I didn’t realize I needed to calibrate. It is such a frustrating experience with my mount that I truly hate doing it.  I did upload my most recent calibration log in my first post if it is of any use in your analysis. 

Fran

[Fran Doherty]

Brian,

Can you expound a little on the unguided Dec behavior? 

If this should be a straight line, it certainly seems like there some an RA effect happening here, as the period of the Dec appears to be pretty much exactly 180 degrees out of phase with RA. In other words the Dec behavior appears to be influenced by RA and is not a random artifact of the data. If this in itself is unusual, would it not be another indication that my mount has issues?

Thanks,

Fran

[Brian Valente]

imo it's a bit of an optical illusion. It may appear Dec axis has issues, but I think what's happening is the RA error is so high, it's causing the star to appear to move in Dec as well. The other possibility is the guiding assembly moved or was rotated, which would invalidate the calibration and also appear as a similar result.

The only way to be sure - and more importantly, to demonstrate to the vendor - is to re-do the calibration so you can show the calibration was recent and was good

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/da4c3bda-5e32-4663-b73c-49719eb01187n%40googlegroups.com.

[Fran Doherty]

Brian,

I did rotate the guiding assembly after the calibration. My OAG is after my rotator, so it moves every time I select a new target. As it remains orthogonal (the OAG is screwed onto the filter wheel which is screwed onto the main imaging camera) I was not worried about this. Is this part of my problem?

Fran

[Bruce Waddington]

Hi guys.  I tried to explain this in my first response on 7/21.  The Dec oscillation you're seeing is almost certainly a consequence of the the huge RA periodic error, and it's what is causing the large orthogonality errors in calibration and high frustration level for Fran. The only way get a calibration with low orthogonality error would be to do the calibration during the inflection points in the RA periodic error curve, and there's no easy way to know when those happen.  And you can't "fix" the problem by using the "assume orthogonal" option in calibration, that will just choose an arbitrary orientation that won't be right in a different phase of the error curve.  It's really a mess.  I suppose you could try to improve the calibration problem a bit by doing a calibration with short exposure times and larger calibration step-sizes in order to minimize the elapsed time of the process.  That can be done by using the 'Advanced' button on the guiding tab and choosing something like 20 pixels of movement and 6 steps.  The Calibration Assistant would squawk about that but you could tell it to ignore the problem.

Bruce

[Brian Valente]

Yes, that is definitely a problem if you aren't connecting your rotator in PHD

Rotating the guider without PHD knowing about it invalidates the calibration.

It doesn't explain the large error in RA, but it's something you need to address

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/93ba378d-5636-46f6-894b-f81c190382ban%40googlegroups.com.

[Bruce Waddington]

Oh Jeez.  You haven't connected PHD2 to a rotator and you didn't tell us you had one.  This casts doubt on the analysis because any rotation of the guide camera relative to the sky invalidates the calibration.  That's why there is rotator support in PHD2.  To run measurement tests, you need to get a usable calibration and leave the rotator in that position.

[Fran Doherty]

Thanks for the information re the rotator. I was unaware I needed to do this. I will connect my rotator routinely now, and will redo my calibration. 

[Fran Doherty]

I truly am sorry. I had no idea re the rotator. I was under the aparently mistaken impression that the same degree of orthogonality was maintained re the main imaging camera, and the calibration remained valid as both main and imaging cameras maintain their sensor positions relative to one another (they are both behind the rotator). Thank you both for all lf the information you have provided me. I will re do everything first chance I get. I hope to not bother you again.

Again, many thanks,

Fran

[Brian Valente]

Fran it's not an issue of guide camera compared with imaging camera

One of the important calibration aspects is it moves the stars in x-y orientation, and then maps that x-y to RA and Dec. In other words, it figures out the rotation of the guide camera *relative to the mount's RA and Dec*. If after the calibration you then rotate the guide camera, you invalidate one of the important calibration results.

It's good you posted this so we can see what's going on and offer feedback

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/ecc1c76f-8bee-4dce-aed6-11a600e7eae9n%40googlegroups.com.