What Constitutes Good Guiding?

[cuivenion]

Pecprep is part of EQMOD but you download it separately. A simpler way to get a pec file is to use Autopec in EQMOD. You can just guide normally and activate recording in autopec, no need to switch off guiding output. Once you have recorded a set number of worm cycles you can start using pec. Autopec also generates a file that can be filtered by PecPrep.

I found this method a bit easier, but it's been suggested that the already suggested method using PHD2 is more accurate. I wouldn't feel qualified to comment on that.

[vlaiv]

I do also believe using PHD2 log and PecPrep to be more accurate.

There are couple of video tutorials on PecPrep - worth looking at (they are short and easy to understand):

If you follow next videos - you will get each part in a row.

 

[Stub Mandrel]

I think a worm cycle for the HEQ5/EQ6 with 144 teeth on the worm wheel is 10 minutes , so I'd hope 30 - 40 minutes would be sufficient?

[vlaiv]

1 hour ago, Stub Mandrel said:

I think a worm cycle for the HEQ5/EQ6 with 144 teeth on the worm wheel is 10 minutes , so I'd hope 30 - 40 minutes would be sufficient?

I believe worm period on HEQ5 is 638s (135 teeth so 10 minutes and 38s) while on EQ6 is smaller (180 teeth, larger worm ) - 479 seconds, or a second under 8 minutes.

Recommended "dose" of PEC is at least 5-6 worm periods, so indeed 40 minutes is minimum for EQ6, but I would not go less than that - it is like regular stacking, more data, greater SNR and more precision in PEC curve.

[Vulisha]

Hi, 

 

I know it is old tread but fits a bill

I got custom 60330 telescope on EQ5 with OnStep and 35/135 guider on -20dec in south. 

 

This are my results from phd2, this is my first guiding, and now I am not sure due to bad resolution,  is this 0.49' or 0.49" error so is it good or it is bad? Can it be better and does it need to be better? 

 

[vlaiv]

16 minutes ago, Vulisha said:

This are my results from phd2, this is my first guiding, and now I am not sure due to bad resolution,  is this 0.49' or 0.49" error so is it good or it is bad? Can it be better and does it need to be better? 

0.49" total RMS is very good value - but I'm afraid - it is not realistic.

0.1s guide exposure is very short guide exposure - most people guide with 1s-2s exposures and those with smoother mounts often use 3s-4s or even longer guide exposures.

Your guider does not have sufficient resolution to measure 0.5" RMS with precision. What is your guide camera? 135mm with usual pixel sizes will give you about 6"/px - and that is too coarse to be able to measure below 1" RMS with precision.

Having said all of that, even if reported figures are not quite correct - I think that you have very good guiding results for EQ5 class mount.

What are your images like? Stars should be round and tight with this guiding results (provided that you image at good resolution - like 1.5"-2"/px).

 

[Vulisha]

Hi Vlaiv,

I am using raspberry Pi HQ camera as a guidecamera and I used Antares as guidestar and I tried with Saturn as well, I am not sure is this from Saturn or Antares, but I believe this one is from Saturn although Antares was similar but disappeared into the night, so pretty bright targets. 

Pixel size iz 1.55 and resolution is 4056x3040

 

Pictures are good, but due to high LP on current location I use short exposures (30sec), so it would probably be good even without guiding, and since I still do not have Bathinov I missed focus a bit, but I want to be ready for dark locations. 

 

See I thought it might be 0.49' as that would be bad but more realistic. I do have Svbony SV105 and and logitech C270 but I did not aim at any star(or planet) with them, HQ cam is much more sensitive. Tonight is cloudy so I cannot test with 1s but I will test that as well, and results with 1s I can consider as realistic? 

[vlaiv]

2 minutes ago, Vulisha said:

Pixel size iz 1.55 and resolution is 4056x3040

Something is wrong with that graph then.

1.55µm pixel size with 135mm FL guide scope gives guide resolution of 2.37"/px

If you look at your stats, 0.08px = 0.40" (I can't really see if it is ' or " - but both are very strange values).

2.37"/px * 0.08px = 0.1896" and not 0.4".

Maybe you used binning for your guide camera? What numbers did you enter for focal length of guide scope and pixel size in PHD2 settings?

[Vulisha]

Yes indeed I did use binning(i think x2)! What resolution that gives?  I entered proper FL and PHD got proper pixel size from INDI. 

 

As this is on RaspberryPi screen I cannot see is it ' or " either, it might be any but I would see big strikes on image then with so much' error. 

 

If I used 60/330 as guide what would then my resolution be? I would like to know RMS and fix my belt or worm if needed to set everything up properly so I don't waste precious night  on dark spot 

Edited August 23, 2021 by Vulisha

[vlaiv]

3 minutes ago, Vulisha said:

Yes indeed I did use binning(i think x2)! What resolution that gives?  I entered proper FL and PHD got proper pixel size from INDI. 

It doubles that of 2.37"px so it is 4.74"/px.

That is good guide resolution for your mount - EQ5 and that mount gives good guiding results even if guide readings might not be as precise.

5 minutes ago, Vulisha said:

If I used 60/330 as guide what would then my resolution be? I would like to know RMS and fix my belt or worm if needed to set everything up properly so I don't waste precious night  on dark spot 

I think that you'll be just fine as is.

[Vulisha]

I found this details it seems. maximum when modded EQ5 can go down to 0.6" when modded by pro, to 1.8" when modded at home and and not modded it is around 8". Mine is  modded by me so 4" seems possible and probablee 

Edited August 23, 2021 by Vulisha

[vlaiv]

6 minutes ago, Vulisha said:

I found this details it seems. maximum when modded by pro EQ5 can go down to 1.8" and not modded it is around 8". Mine is  modded by me so 4" seems possible and probable. 

I think you missed by order of magnitude

Above chart says that Home Modded EQ5 drive is able to be guided at 1.8" RMS while your PHD2 reported 0.4" RMS - which is about x4 lower RMS. Even DarkFrame tuned version does not guide as low as 0.4" RMS - 0.6" RMS is quoted.

In any case - your guiding is good even if it is not measured quite accurately.

[JonCarleton]

I've noticed something on PHD2 YouTube videos.  Apparently, if you set the scale all the way up to 16, it really smooths out the graph!  

 

[Vulisha]

You sure about that 😅

 

I changed camera to svbony sv105 3um pix on 1920x1080. and now I got this messed up errors, could it be that my belts are not tight enough so it results in this mess? Or something else? 

 

I doubt it is balancing since scope and counterweights together have around 4kg on EQ5, But my counter weights are "hanging" (4x0.5kg weightlifting counterweights as original eq5 is too heavy for this small scope) 

Edited August 31, 2021 by Vulisha

[Stub Mandrel]

On 23/08/2021 at 20:34, Vulisha said:

I found this details it seems. maximum when modded EQ5 can go down to 0.6" when modded by pro, to 1.8" when modded at home and and not modded it is around 8". Mine is  modded by me so 4" seems possible and probablee 

Hmm.

I 'tuned' my HEQ5 rather than 'modding' it and have got as low as 0.6".

I've since fitted a Rowan kit but have only used it for planetary since. To be honest, I think the biggest issue is getting the worm gear engagement right.

 

[StuartT]

On 26/06/2018 at 12:37, vlaiv said:

I turn off guiding and use PHD2 to create log file (there is option in PHD2 to disable guide commands). I usually create about hour / hour and a half of log file. While doing that - at some point I press time stamp button in EQMod. EQMod auto PEC is also turned off. Next I load PHD2 log data into PecPrep and create PEC curve.

 

Hi @vlaiv sorry to be late to the party here, but I am just getting to grips with PEC. I am curious as to why you say guide commands have to be switched off? I have just analysed a PHD2 log file and analysed in PECPrep with only the 'auto filter' added. Here is what I got. The PEC curve is created is not a pure sine wave, but has a higher frequency oscillation (period 11, mag 33.4) added to the main worm gear period (period 198.7 mag 100). Is it ok to load a curve like this into EQMOD? Thanks!

(or is it just easier to let PHD2 do everything by selecting the 'predictive PEC' algorithm as Cuiv recommends?)

Edited January 29, 2023 by StuartT

[vlaiv]

10 minutes ago, StuartT said:

I am curious as to why you say guide commands have to be switched off?

Point of PEC is to produce correction of the mount as mechanically is - without any external aids - like guiding.

This will make mount run smoother and will put less strain on guider system once you start using it.

Guide corrections will mask true underlying shape of PE curve and produced PEC will be sub optimal (even if you apply it with guiding only).

[StuartT]

23 minutes ago, vlaiv said:

Point of PEC is to produce correction of the mount as mechanically is - without any external aids - like guiding.

This will make mount run smoother and will put less strain on guider system once you start using it.

Guide corrections will mask true underlying shape of PE curve and produced PEC will be sub optimal (even if you apply it with guiding only).

Thanks for this. Can I ask what you think of the alternative approach - using the 'predictive PEC' algorithm in PHD2? I hear it's very effective

[vlaiv]

3 hours ago, StuartT said:

Thanks for this. Can I ask what you think of the alternative approach - using the 'predictive PEC' algorithm in PHD2? I hear it's very effective

I haven't tried that one (that I remember), but in essence - it should be close in performance as it relies on same things.

Same way you can hit "auto" in PecPrep to get the curve (it tries to remove noise and insignificant harmonics and isolates important stuff) - it can be done in PHD2, after all - they have access to same raw data (PHD2 can record position prior to issuing correction).

There are only two things that are different:

- predictive pec needs some time to learn and it won't give you best performance from the start of the guiding sessing

- PHD2 relies on corrections being followed to the letter - and that might not be the case. In each new round of correction, in order to get "uncorrected" behavior of the mount - PHD2 needs to mathematically reverse last correction and figure out where the mount would be without correction issued (so it can get accurate reading on periodic error). Problem is - corrections are not perfect. Sometimes they overshoot, sometimes they undershoot - no way of knowing how much of a correction was taken up by the mount (backlash and other mechanical issues).

For this reason I would give slight edge to the PEC recording and preparation as it can use multiple PE periods to establish good mean periodic error and correction will be applied from the start regardless if one is guiding or not.

[StuartT]

1 hour ago, vlaiv said:

I haven't tried that one (that I remember), but in essence - it should be close in performance as it relies on same things.

Same way you can hit "auto" in PecPrep to get the curve (it tries to remove noise and insignificant harmonics and isolates important stuff) - it can be done in PHD2, after all - they have access to same raw data (PHD2 can record position prior to issuing correction).

There are only two things that are different:

- predictive pec needs some time to learn and it won't give you best performance from the start of the guiding sessing

- PHD2 relies on corrections being followed to the letter - and that might not be the case. In each new round of correction, in order to get "uncorrected" behavior of the mount - PHD2 needs to mathematically reverse last correction and figure out where the mount would be without correction issued (so it can get accurate reading on periodic error). Problem is - corrections are not perfect. Sometimes they overshoot, sometimes they undershoot - no way of knowing how much of a correction was taken up by the mount (backlash and other mechanical issues).

For this reason I would give slight edge to the PEC recording and preparation as it can use multiple PE periods to establish good mean periodic error and correction will be applied from the start regardless if one is guiding or not.

as usual a well-informed and helpful answer. Thank you! 

So in order to get the best raw data for analysis in PECPrep should I just run the guiding asst for a while? Presumably that will just be the mount behaviour without guide pulses?

[ONIKKINEN]

Predictive PEC has worked for my mount on all but one occasion where i bumped the mount and i think it may have affected the prediction algorithms somehow. In that case the predictive correction happened too early and actually caused a spike rather than fixed it (below you see the correction happens before the spike, so the correction actually caused it).

This spike is about 4'' in magnitude and in all other cases this disappears so the prediction algorithm seems to do its job well for my AZ-EQ6 with a not so great RA worm.

[vlaiv]

2 hours ago, StuartT said:

So in order to get the best raw data for analysis in PECPrep should I just run the guiding asst for a while? Presumably that will just be the mount behaviour without guide pulses?

Just run PHD2 like you normally would - except that you disable guide output.

There is a checkbox somewhere in the settings that you should uncheck. PHD2 will continue happily doing its thing, but not corrections will actually be sent to the mount.

Afterwards - you just take guide log and use that in PecPrep.

Here is the setting I'm talking about:

just remember to turn it back on after you've finished recording pec data.

[oymd]

Sorry to intrude on the thread, but I want to understand PEC recording and how to apply it to my mount.

I am troubleshooting my CEM40, which seems to behave badly in RA, immediately as I start PHD2. It jumps to RMS 1.5 in a matter of 1-2 seconds, NO MATTER WHAT I DO.

Mechanically I stripped the mount, changed the belts, have the bearings on order, but still the same behavior.

Tried fine tuning the mesh binding between the worm and gear, improved the DEC backlash significantly from >65000ms to about 400ms, get good PHD2 CALIBRATION results, but RA is hopeless. Never better than 1.2RMS

With regards to PEC recording and applying, what should I do?

In IOPTRON Commander, there is the option to RECORD PE.

There is also an option to PLAY BACK the PE.

When, how and how long do I PLAYBACK the PEC?

From the above, my understanding is to record PE when the mount IS NOT GUIDING or connected to PHD2?

My work period is 400s, but in PHD2 it auto corrects to about 800s, when I choose the PPEC alogorithm for RA guiding

@vlaiv

Vlaiv, would be great if you can help me with this?

How to I apply the PEC that I record in Ioptron Commander to my mount's guiding?

I've run the PEC recording while guiding, whoile NOT guiding, with PHD2 closed, and it seems to give me random results.

I do not have PEMPRO, which I read that is needed for applying PEC recording to the mount's guiding?

Imaging is at 350fl, 294MC Pro had 4,63micron pixels, so imaging scale is 2.7"/pixel.

Starts are more or less round, and I am actually surprised that the subs look much better than what you would expect when ;looking at the graphy on PHD2, but I know something is wrong.

Guide scope is the SW Evoguide, 242FL, camera is 120MM Mini 3.75micron, so guiding at 3.2"/pixel

Sorry, so so confused?

[drjolo]

14 minutes ago, oymd said:

Sorry to intrude on the thread, but I want to understand PEC recording and how to apply it to my mount.

I am troubleshooting my CEM40, which seems to behave badly in RA, immediately as I start PHD2. It jumps to RMS 1.5 in a matter of 1-2 seconds, NO MATTER WHAT I DO.

Mechanically I stripped the mount, changed the belts, have the bearings on order, but still the same behavior.

Tried fine tuning the mesh binding between the worm and gear, improved the DEC backlash significantly from >65000ms to about 400ms, get good PHD2 CALIBRATION results, but RA is hopeless. Never better than 1.2RMS

These spring loaded CEM40, CEM26 and similar mounts are very susceptible to perfect balancing - in RA, Dec, but also along the telescope axis. So if you have heavy focuser motor or guide scope on the side, it needs to be balanced on the opposite side of the OTA. Worm gear tension needs to be adjusted as light as possible to cancel the play, but no more. Stepper motors in these mounts are undersized and such behavior may be a reason of accumulation of microsteps that are released after some time. 

[vlaiv]

29 minutes ago, oymd said:

My work period is 400s, but in PHD2 it auto corrects to about 800s, when I choose the PPEC alogorithm for RA guiding

@vlaiv

Vlaiv, would be great if you can help me with this?

How to I apply the PEC that I record in Ioptron Commander to my mount's guiding?

I've run the PEC recording while guiding, whoile NOT guiding, with PHD2 closed, and it seems to give me random results.

I do not have PEMPRO, which I read that is needed for applying PEC recording to the mount's guiding?

Ok, so if you are using iOptron commander - it is different from using EQMod.

You won't be doing PE curve preparation - mount will do that for you, or rather iOptron commander will do that for you. In this case - it must know what the needed corrections are and you need to start guiding when you hit PEC record. Commander will track where mount is supposed to be - but it will also track corrections and from the two will derive PEC curve.

You need to keep it like that for at least couple of PE cycles - let's say 5 cycles - that is 2000 seconds total, so just a bit more than half an hour.

Once you are done - when you next start RA tracking, regardless if you are guiding or not - you can hit PEC playback and it will apply recorded correction to the mount. It should keep that PE correction until you record a new one - so you should be able to reuse it very session by playing it back.

As far as 1.2" RMS - that is quite a lot, and there are couple of things that you should look into:

1. Do above advice on balancing your setup

2. See if your clamping connection is strong enough for the scope - you might need to improve that

3. You should have virtually zero backlash since you have spring loaded gears - make sure you've tuned that properly in both axis

4. Make sure your tripod is sturdy enough and have been placed on ground where it can't move - don't put it on soft ground like sand - or if you do - try to "dig it in" a bit so it is rock solid. If it has extending legs - don't extend them fully - you don't need your setup to be at "observing" position for imaging. It can be lower than that.