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Which PH2D algorithms do you use?

Astrophotography Equipment Mount Software
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#1 marvyyk

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Posted 13 May 2022 - 07:10 AM

Hi All! 

 

Quick question, which guiding algorithms do you use in PH2D for RA and DEC? And why?? 

I use the default ones... 

 

Clear skies!

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#2 KC_Astro_Mutt

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Posted 13 May 2022 - 07:55 AM

I'm looking into this as well. Thanks for the post! Interested to read the responses.


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#3 Tapio

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Posted 13 May 2022 - 08:04 AM

Predictive PEC is good in RA.
Otherwise defaults work.
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#4 F.Meiresonne

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Posted 13 May 2022 - 08:20 AM

I use defaults too. I never had problems with guiding. It worked out of the box, so why try to solve problems one does not have.


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#5 bobzeq25

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Posted 13 May 2022 - 08:41 AM

PPEC works very well on my CEM60.  I never use anything else.

 

DEC can vary, depending on sky location.  I sometimes use resist switch, sometimes guide in only one direction.  Have been known to work on unusually good polar alignment (Sharpcap Pro) and turn DEC off altogether.  These decisions are frequently made "on the fly".

 

I now only use multistar.


Edited by bobzeq25, 13 May 2022 - 08:42 AM.

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#6 unimatrix0

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Posted 13 May 2022 - 08:42 AM

PHD2 recommended me to switch to "resist switch", whatever that means. 

 

I also tried PPEC, both works ok, although the longer you use PPEC, the more PHD2 learns about your mount errors and start to predict when to apply correction. 


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#7 DirtyRod

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Posted 13 May 2022 - 08:57 AM

PPEC and Resist Switch work best on my Celestron mounts.


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#8 michael68

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Posted 13 May 2022 - 08:58 AM

I've played with every setting in PHD2 and my mount in the quest for the ultimate guiding. I tuned and re-tuned. tinkered and tested. Wasted dozens of beautiful clear sky hours staring at the graph.

At the end of it all, I created a new profile, left everything default besides applying the recommendations from GA and now.. best guiding I've ever had on my cem40.

I guess some people have to learn how it got it's name the hard way? 


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#9 marvyyk

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Posted 13 May 2022 - 07:41 PM

Thanks for you replies and shared experience!

 

I own a CEM26, I get often under 1" RMS total error... But something my DEC graph gets funky or crazy... Since I have a Zenithstar 73 and FL of 430mm (px scale 2,28"), guiding under 1" is quiet ok and my stars are round. 

 

But it is interesting to read other experience and learn from it! waytogo.gif  
 

Cheers, and clear sky!



#10 michael68

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Posted 13 May 2022 - 09:27 PM

I gotta say, I've seen allot of folks on both sides of the fence on the topic of calibrating once and forgetting it vs. calibrating often but my personal experience, recalibrating when I move to a new target seems to keep things consistent with PHD2 and my mount. I mentioned this before on CN that when I calibrate at the equator and start guiding my guiding is fantastic. and as long as I stay in that vicinity, It stays that way. But if I move towards the zenith, things go crazy. 

Like my mount is bipolar! (no pun intended! grin.gif ) My DEC goes from under 0.5 px corrections to 1.5. Stars are enlongated and bloated. But once I calibrate in that spot, it settles down again and starts behaving. 

I just downloaded the NINA 2.0 Beta just so I can force PHD2 to recalibrate in my sequences. 

Some people say, "You don't have to recalibrate after your first time." What they mean is THEY don't have to. I clearly do and my images seem to agree. 

If your guiding gets weird, particularly when you've done a big slew,  give recalibration a try. If nothing else, it won't make it worse. 


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#11 Der_Pit

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Posted 14 May 2022 - 08:55 AM

As others said, for RA use PPEC, and make sure guiding runs for some 10-20 minutes before you start imaging.

For DEC it depends on whether you have backlash.  Without, the default hysteresis is fine, else resist switch is a good option.

 

@michael68: My first suggestion would be to carefully check (3D) balancing of the OTA if guiding is strongly position dependent.


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#12 michael68

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Posted 14 May 2022 - 10:02 AM

@michael68: My first suggestion would be to carefully check (3D) balancing of the OTA if guiding is strongly position dependent.

Nah, it's not the balance. I've played it all different ways. Perfectly balanced, favoring the east, favoring the camera or both. I do have the 3rd axis counterweight for the ioptron as well. None of that helped. Recalibrating is the only thing that made a difference. I know it seems counter-intuitive... I mean... the sky all moves at the same rate, in the same direction, right? But that's precisely what got me thinking. My scope is mounted on a perm pier. Polar alignment error consistently measures under a minute. The star shouldn't drift at all in DEC but that axis was going wild. Furthermore, in my "experiments" my stars looked better when I disabled guiding at the zenith than with PHD2 guiding. I was conclusive. The mount wasn't giving me poor guiding. PHD2 was.

And even then, I wasn't convinced about how to fix it until I read Craig Stark himself state: "If you slew to a different portion of the sky, the vectors PHD uses must be updated by running the calibration again." So That's what I tried and it clearly worked. As long as I calibrate after I slew, my corrections on both axis stay under 0.5 px. And that's with all default PHD2 settings aside from the DEC backlash and Minmove recommendations from GA. Even considerable imbalances are well tolerated, surprisingly.

This is classic "Forest for the trees" stuff. We want so bad for there to be some complex reason for the bad guiding that we overlook the easiest solution. 


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#13 nebulasaurus

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Posted 14 May 2022 - 10:17 AM

And even then, I wasn't convinced about how to fix it until I read Craig Stark himself state: "If you slew to a different portion of the sky, the vectors PHD uses must be updated by running the calibration again." So That's what I tried and it clearly worked.

This is not necessary with PHD2.  PHD2 will rotate the guiding vectors for both changes in declination and changes in camera angle due to use of a motorized rotator.  Of course, that only applies if you are guiding via the mount via ASCOM and have an ASCOM compliant rotator that will report position.

 

I slew to the east somewhere near Dec +20 at the start of an evening and calibrate the guider.  Then wherever I slew, and whatever I rotate the camera to, guiding just works.

 

If you find you have to recalibrate with changes in Dec with PHD2 then you are either guiding via an ST-4 style cable, or there is some other root cause you need to be looking for.


Edited by nebulasaurus, 14 May 2022 - 08:18 PM.

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#14 dciobota

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Posted 14 May 2022 - 10:48 AM

To throw in my two pennies, and this might shed some light on Michael's issue as well.

 

I tried ppec, and it works with my mounts (az-gti and az-gte in eq mode) but, only if I don't reach the payload limit.  If I do, what happens is even a slight imbalance causes torsional loads to affect the motor speed, as it gets close to its stall point.  Remember, even with a counterweight, you are still moving all that mass, and for a motor close to the load limit it can definitely affect its speed.  At least that's been my experience anyway.  This will affect the PPEC corrections, as the phase shifts and even the amplitude and profile of PE can shift as well.  

 

So, I use the standard algorithm now, can't remember the name of it, and it works fine.  It does seem to adapt to these changes in PE profile, although I have had a couple nights when things went haywire for some unknown reason.

 

For dec, I use resist switching, as even if you imbalance in dec, that balance will shift as you cross the meridian.  And yes, I use multistar, although in my case it's not made a whole lot of difference in guiding accuracy.

 

I should correct myself and say, all this I used to do.  Now I use asiair units, and no clue what algorithms they use, but the end results seem to be the same.

 

Hope this helps.


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#15 michael68

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Posted 14 May 2022 - 11:20 AM

Yeah, all good points. And yes, I think it all helps the OP. I think the important thing is that there is not one perfect algorithm. Just too many variables. Re-calibrating (as I've said) may not be required for everyone. Trust me, I don't want to do it. It eats up valuable time. And For sure it might be some other weird flexure issue, imbalance, chip tilt, gravity, geez, the list of possibilities seems infinite. But I'm not going to chase each of these down. Recalibrating in the vector of sky works for me. The proof is in the image. So let the scope flex all it wants. Let the balance shift a little after a flip or whatever else might be the root cause. I've found one solution that works for my particular issue and it's not going to work for everyone. But let's not call it unnecessary. Because without knowing all the contributing factors, that's inconclusive. I know for me to get through a night of imaging multiple targets and not chasing down every ghost in the machine  (which I think is impossible because they're evolving) for me, recalibrating is necessary.

I've played with PHD2 and all it's options for a long time chasing issues. and I didn't seem to resolve things. At times I definitely made things worse and all the while, not capturing DSO images which is exactly what I'm out there for.

The moral of the story for the OP. We can all tell you what algorithms we use. Take it with a grain of salt. It's not an implication that PPEC, Hysteresis, resist switch or any other setting is the one you need to use. Great discussions fellows. Thank you!


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#16 kathyastro

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Posted 14 May 2022 - 11:25 AM

PPEC and Resist Switch for my CEM-60.  Lately, my RMS has been down around 0.7".


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#17 Der_Pit

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Posted 14 May 2022 - 11:43 AM

Nah, it's not the balance. I've played it all different ways. Perfectly balanced, favoring the east, favoring the camera or both. I do have the 3rd axis counterweight for the ioptron as well. None of that helped.

 That 3rd axis counterweight - where is it?  And what Mount?  with the CEMs you cannot 3D balance the OTA with a side weight on the CW/CWB, as that one doesn't rotate with DEC,  So any imbalance of the setup has to be balanced on the telescope side

 

Recalibrating is the only thing that made a difference. I know it seems counter-intuitive... I mean... the sky all moves at the same rate, in the same direction, right?

Yes and no.  The angular rotation speed is constant, yes, but the actual speed 'on sky' scales with the cosine of the declination.  PHD2 should compute this automatically from the calibration and the actual position.  The only reason that isn't working would be wrong or missing pointing information.  

Heck, I've taken my mount off the pier for the winter, put it back in March an started guiding at 0.3" RMS, with the calibration from the year before.... (that's with EKOS though, not with PHD2)

 

But that's precisely what got me thinking. My scope is mounted on a perm pier. Polar alignment error consistently measures under a minute. The star shouldn't drift at all in DEC but that axis was going wild.

So does it drift? With 1' PA it should take minutes before a correction is needed.  

 

Furthermore, in my "experiments" my stars looked better when I disabled guiding at the zenith than with PHD2 guiding. I was conclusive. The mount wasn't giving me poor guiding. PHD2 was.

With 'at zenith', do you refer to changing the target, or tracking a target that goes through zenith?  If it is (also) the latter,  then it's not PHD2, because in that case the guide parameters do not change.  If still the re-calibration does help that would indicate that the guide speeds have changed, for me indicating that the stepper motor is losing steps - and that most likely because of too high load due to some inbalance (sorry to insist blush.gif ). 

Or, if it's one of the ioptrons with magnetic meshing: It could be that the meshing is too tight or too loose.  I do have issues with that, too (CEM60EC).  My DEC axis wheel is slightly excentric, and in some places the worm can bind and stall the motor if the knob is too tight. I'd check this, slew the mount with the hand panel at high speed through the whole range and check if the meshing is too tight or too loose anywhere.


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#18 michael68

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Posted 14 May 2022 - 04:44 PM

 That 3rd axis counterweight - where is it?  And what Mount?  with the CEMs you cannot 3D balance the OTA with a side weight on the CW/CWB, as that one doesn't rotate with DEC,  So any imbalance of the setup has to be balanced on the telescope side

Capture.JPG

This is how the 3rd axis CW is mounted. While this is a stock photo on a cem70, mine is mounted on  my CEM40.

 

Yes and no.  The angular rotation speed is constant, yes, but the actual speed 'on sky' scales with the cosine of the declination.  PHD2 should compute this automatically from the calibration and the actual position.  The only reason that isn't working would be wrong or missing pointing information.  

Heck, I've taken my mount off the pier for the winter, put it back in March an started guiding at 0.3" RMS, with the calibration from the year before.... (that's with EKOS though, not with PHD2)

Not disagreeing with you on any of this. PHD2 SHOULD be compensating. But it's not. I'm not making this stuff up. Guiding corrections on both axis on the equator are less than 0.5px.

 

 

So does it drift? With 1' PA it should take minutes before a correction is needed. 

It usually doesn't. I drift aligned using PHD2 and really tried getting it dialed in. My last GA ran about 12 minutes and PA error was reported at 0.8". On the equator, the DEC didn't correct much my last time out and when it does the pulses were short making corrections of about 0.3-0.5 px. But it doesn't go minutes with corrections, but close to a minute.

 

 

 

With 'at zenith', do you refer to changing the target, or tracking a target that goes through zenith?  If it is (also) the latter,  then it's not PHD2, because in that case the guide parameters do not change.  If still the re-calibration does help that would indicate that the guide speeds have changed, for me indicating that the stepper motor is losing steps - and that most likely because of too high load due to some inbalance (sorry to insist blush.gif ). 

Moving to the Zenith. For example moving from the equator and going to M51 or M101. So this is the important distinction. As soon as I move there and start guiding, I start getting DEC pulses between 1-2px almost consecutively. And that's right after coming from the equator getting 0.3-0.5 px every 45-60 seconds. The last few tests, I calibrated after the slew and I was getting great guiding again at the zenith. And again not very many corrections.

Don't apologize! I think we're all here trying to learn and help one another... (Although I do apologize to the OP for kinda highjacking his thread!). Incidentally, a small imbalance has been recommended many times so which is it? Is perfect balance the objective or a purposeful imbalance? Frankly I thought the imbalance approach was for gears not belts  but I've tried both. Right now, I'm as perfectly balanced as I can get it. As for max limits, Things are heavy, no doubt. With my SVX, guide scope, cameras, dovetail plates, scope rings, NUC, etc, looking at about 22 pounts. For a mount rated for 40 max. Don't know how over worked the mount is. 

 

 

 

Or, if it's one of the ioptrons with magnetic meshing: It could be that the meshing is too tight or too loose.  I do have issues with that, too (CEM60EC).  My DEC axis wheel is slightly excentric, and in some places the worm can bind and stall the motor if the knob is too tight. I'd check this, slew the mount with the hand panel at high speed through the whole range and check if the meshing is too tight or too loose anywhere.

Yeah... could be any of those things. But this is where I start getting into less is more. If I can improve my results by simply recalibrating, why go through all the trouble of trying to eliminate flexure the size of a tenth of a human hair or a overly tightened belt on my DEC motor or even the smallest imbalance on one side of the mount or another? Recalibrating is giving me great results regardless of whether it's the right way or not. While I appreciate the intentions, and I do, I will just use this until it stops working. laugh.gif


Edited by michael68, 14 May 2022 - 04:46 PM.

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#19 marvyyk

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Posted 14 May 2022 - 08:28 PM

 That 3rd axis counterweight - where is it?  And what Mount?  with the CEMs you cannot 3D balance the OTA with a side weight on the CW/CWB, as that one doesn't rotate with DEC,  So any imbalance of the setilup has to be balanced on the telescope side

 

 

Here's what I did to "3D" balanced my Dec on my CEM26: a couple washers attached to the dovetail... So far it works very well! Easy to make and cheap, just visit any home hardware!

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  • 3D_Capture.JPG

Edited by marvyyk, 14 May 2022 - 08:28 PM.



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