Using PEC while guiding? Cem60

[AntMan 72]

I have been finding conflicting opinions & suggestions regarding this question on the internet even from Ioptron. Some say it fights each other others it complements each other. I want to know what the guys responsible for this great software have to say. 

[Brian Valente]

Hi Antman,

 

I’m not sure what is the debate. They both contribute to better imaging in different and complementary ways.

 

The problem imo is PEC and guiding can be tricky to understand and implement correctly, and if you do one or the other poorly, it could make things worse. Usually when I see complaints or issues (myself in the past included) it’s because of lack of understanding or bad implementation.

 

 

 

But here’s the basic idea on how they work together:

 

1.       Pretty much all mounts have some amount of periodic error(s)

 

2.       Periodic error correction (PEC) smooths those out as much as possible at the mount.

 

3.       But PEC probably won’t get rid of all periodic error. There is residual error

 

4.       Guiding then “takes it the rest of the way” by not only compensating for the mount’s errors, but also compensating for other challenges like polar alignment errors, etc.

 

5.       However, guiding is not magical. If your mount has large periodic errors, guiding may not be able to compensate for that. That is why you want PEC

 

 

I can only think of limited reasons why you wouldn’t want to use both:

 

1.       You messed up PEC and it made things worse

2.       You are imaging at such a low resolution that it wouldn’t make any difference

3.       You have a mount with such good PE that it isn’t required (note: if you do, please tell me the make and model!)

 

 

 

 

Thanks

 

Brian

 

 

Brian Valente

Brianvalentephotography.com

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[Brendan Kinch]

1.       You messed up PEC and it made things worse

2.       You are imaging at such a low resolution that it wouldn’t make any difference

3.       You have a mount with such good PE that it isn’t required (note: if you do, please tell me the make and model!)

4. Your mount won't accept PEC......(e.g. Takahashi)

As far as I know anyway.....

Kinch       

[Brian Valente]

Yes – true!

 

And other simple mounts like ioptron skytracker, etc. (which can take ST-4 guiding but otherwise are pretty rudimentary)

 

 

Thanks

 

Brian

 

 

Brian Valente

Brianvalentephotography.com

 

From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Brendan Kinch

Sent: Tuesday, February 27, 2018 12:48 PM
To: Open PHD Guiding <open-phd...@googlegroups.com>

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[AntMan 72]

I understand the concept but can you suggest a tutorial on the correct way to implement both so they complement each other. Many posts out there suggest a lack of knowledge on this subject which is why i posted it here & not CN.

[peter wolsley]

PHD2 offers a PPEC algorithm with is designed to provide both guiding and PEC as a fully integrated solution.  There are lots of people here who can help you implement PHD2s PPEC algorithm. 

I also would suggest reading up on how to implement PEC specifically for your CEM60.  Read your manuals and familiarize yourself with how this is done using your specific mount.  Every vendor is going to be slightly different and you want to avoid that confusion.  Implementation can even vary between models from a single vendor.  You could ask on CN for CEM60 specific help.  Many people struggle with this...be prepared to experience a learning curve with this subject.

Peter 

[AntMan 72]

Hi, I am pretty confident in mount PEC dept but not in PHD2 and what i should do differently compared to guiding without pec enabled? I have used Pempro and measured my PE curve but the program does not support uploads to my mount. I am going to use the Pec record option in the hand controller tonight if i get clear enough sky's. I see you mentioned Predictive pec in phd2. Is this the setting you would recommend over the default hysteresis? Also are there any other starting parameters you can recommend once my pec on the mount is complete?

Thank you all for your time

Anthony

[Brian Valente]

My recommendation is to run some guiding along the lines of what I mentioned before and upload the guide log and debug log. Just use the defaults for now re: guiding algorithms

 

That would give us a place to start with feedback.

 

Thanks

 

Brian

 

 

Brian Valente

Brianvalentephotography.com

 

From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of AntMan 72
Sent: Tuesday, February 27, 2018 1:58 PM
To: Open PHD Guiding <open-phd...@googlegroups.com>
Subject: [open-phd-guiding] Re: Using PEC while guiding? Cem60

 

Hi, I am pretty confident in mount PEC dept but not in PHD2 and what i should do differently compared to guiding without pec enabled? I have used Pempro and measured my PE curve but the program does not support uploads to my mount. I am going to use the Pec record option in the hand controller tonight if i get clear enough sky's. I see you mentioned Predictive pec in phd2. Is this the setting you would recommend over the default hysteresis? Also are there any other starting parameters you can recommend once my pec on the mount is complete?

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[bw_msgboard]

Hi Anthony.  It sounds like you might want to take a look at this in addition to what others have said (use of PEC is included):

 

https://openphdguiding.org/phd2-best-practices/

 

Have fun,

Bruce

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of AntMan 72
Sent: Tuesday, February 27, 2018 1:58 PM
To: Open PHD Guiding
Subject: [open-phd-guiding] Re: Using PEC while guiding? Cem60

 

Hi, I am pretty confident in mount PEC dept but not in PHD2 and what i should do differently compared to guiding without pec enabled? I have used Pempro and measured my PE curve but the program does not support uploads to my mount. I am going to use the Pec record option in the hand controller tonight if i get clear enough sky's. I see you mentioned Predictive pec in phd2. Is this the setting you would recommend over the default hysteresis? Also are there any other starting parameters you can recommend once my pec on the mount is complete?

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[AntMan 72]

Bruce, I read through the best practices guide. I was looking for specific information on why so many people seem to fail to get phd2 to work with there pec on all different mounts. I did not want to waste my time failing as the majority seem to do. It seem there is no specific answer as to why many can not get them to work together.

Thanks,

Anthony

[bw_msgboard]

Hi Anthony.  I suspect the problem is not that the two don’t “work together”.  I think it’s more likely that the PEC is being done incorrectly in the first place or no longer reflects the behavior of the mount.  There really isn’t any sense of “working together” – the PE correction done in the mount controller happens first, long before PHD2 takes another exposure and measures the position of the guide star.  So when the PE curve is correctly programmed and applied, the mount simply looks to PHD2 like a mount that tracks better.

 

Unfortunately, there are various ways for people to get tripped up trying to apply a PE correction curve:

1. The curve must be computed by a PEC application, it can’t be done effectively by hand while squinting through an eyepiece.  The application should measure the behavior over multiple worm cycles, then apply some statistical techniques to discard outliers (bad seeing, mount bumps, wind gusts) and correct for drift.
2. PE correction in the mount can normally only deal with integer harmonics of the worm period, and trying to correct for other frequencies (over-programming the PE) can makes things worse.
3. Once the PE curve is uploaded to the mount, it’s important to measure the tracking again with PEC enabled.  In some cases (for reasons I’ve never learned), the curve may be inverted, meaning the tracking is actually worse than before.  In other cases, the mount vendor may have botched the implementation of PEC altogether.  So you’ll always want to have a “before” and “after” view of the RA tracking to be sure that you’ve actually improved things.

 

Even after a good PE curve is applied, it usually won’t last forever.  Mount behavior can change over time because of gear wear (wear-in) or because of mechanical adjustments made by the user.  If the PE curve gets out of phase from the actual tracking of the mount, the accuracy can again get worse.  

 

Hope this helps,

[Bryan]

I do not believe that PPEC does full PEC.  It is a guiding algorithm that will try to offset RESIDUAL PE, among other errors.  The majority of the PE should be taken out with the mount's inherent PEC technique.

The Detailed Info on PPEC is at

https://openphdguiding.org/manual/?section=Guide_algorithms.htm#Guide_Algorithm_Parameters

Scroll down to PPEC.  In particular, see the paragraphs on time-scales (short, medium, long)

Bryan

On Tuesday, February .  IN particuar, see the SHort algorithm with is designed to provide both guiding and PEC as a fully integrated solution.  There are lots of people here who can help you implement PHD2s PPEC algorithm. 

[AntMan 72]

This is what i was looking for.  I see all these people failing at using the two methods together and my brain needs to know why so i do not make the same mistakes. There is much false info out there telling us the two do not behave well together. Thank you for the information Bruce. I realy do appreciate it.

Anthony

[bw_msgboard]

Ok, glad it made sense.  The truth is, we don’t see much of this on the PHD2 forum, so I’m not really aware of how common it is for people to have PEC-related problems.  You are right about all the bogus info that’s out there, it can be a little discouraging.  On this forum, we typically spend a lot of time looking at guiding data from end-users and we use that to try to help them get better results.  I think one of the biggest sources of misinformation on some of the astro forums is people trying to offer solutions without having looked carefully at the data to understand what the underlying problem really is.  Anyway, we’ll be happy to help you out as you move forward.

 

Bruce

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of AntMan 72
Sent: Tuesday, February 27, 2018 4:57 PM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] Re: Using PEC while guiding? Cem60

 

This is what i was looking for.  I see all these people failing at using the two methods together and my brain needs to know why so i do not make the same mistakes. There is much false info out there telling us the two do not behave well together. Thank you for the information Bruce. I realy do appreciate it.

 

Anthony

On Tuesday, February 27, 2018 at 6:32:35 PM UTC-5, Bruce Waddington wrote:

Hi Anthony.  I suspect the problem is not that the two don’t “work together”.  I think it’s more likely that the PEC is being done incorrectly in the first place or no longer reflects the behavior of the mount.  There really isn’t any sense of “working together” – the PE correction done in the mount controller happens first, long before PHD2 takes another exposure and measures the position of the guide star.  So when the PE curve is correctly programmed and applied, the mount simply looks to PHD2 like a mount that tracks better.

 

Unfortunately, there are various ways for people to get tripped up trying to apply a PE correction curve:

1.      The curve must be computed by a PEC application, it can’t be done effectively by hand while squinting through an eyepiece.  The application should measure the behavior over multiple worm cycles, then apply some statistical techniques to discard outliers (bad seeing, mount bumps, wind gusts) and correct for drift.

2.      PE correction in the mount can normally only deal with integer harmonics of the worm period, and trying to correct for other frequencies (over-programming the PE) can makes things worse.

3.      Once the PE curve is uploaded to the mount, it’s important to measure the tracking again with PEC enabled.  In some cases (for reasons I’ve never learned), the curve may be inverted, meaning the tracking is actually worse than before.  In other cases, the mount vendor may have botched the implementation of PEC altogether.  So you’ll always want to have a “before” and “after” view of the RA tracking to be sure that you’ve actually improved things.

[Brian Valente]

Bruce offers some good advice Anthony

 

The other thing I’d offer is that rarely do things go as planned: nothing ever seems to work as it should, and it sometimes works differently the second time, even when it appears nothing has changed. A lot of people get exasperated and give up. I took a three year hiatus!

 

If you go slowly through each of PEC and guiding and really understand what it does and why it does or does not do what you want, you’ll be better for it and you’ll get better results, individually and together.

 

Bruce and Andy offer amazing support for openPHD. Once you get to your guiding part, I really encourage you to post your logs and ask for feedback.

 

 

 

 

 

Thanks

 

Brian

 

 

Brian Valente

Brianvalentephotography.com

 

[Brian Valente]

Correct – PPEC algorithm only addressed the main harmonic, and learns as it goes (if you restart guiding it has to start over learning).

 

It’s a great companion to true PEC, but not a replacement.

 

 

 

 

Thanks

 

Brian

 

 

Brian Valente

Brianvalentephotography.com

 

From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Bryan

Sent: Tuesday, February 27, 2018 3:38 PM
To: Open PHD Guiding <open-phd...@googlegroups.com>

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[AntMan 72]

I don't think i enabled logging unless in enabled by default but can you guys tell anything from this picture and whatever advise you can give. No PEC just guiding . I didn't want to start a new thread... Thanks in advance..

[Brian Valente]

Hi Anthony – it’s enabled by default. This will help you find your log:

 

https://openphdguiding.org/getting-help/

 

Thanks

 

Brian

 

 

Brian Valente

Brianvalentephotography.com

 

[AntMan 72]

Bruce, can i have your permission to share this important information you posted on CN? So others can find it and stop regurgitating false info.

[bw_msgboard]

Hi Anthony.  That’s fine with me – for whatever it’s worth. <g>

 

Bruce

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of AntMan 72
Sent: Sunday, March 04, 2018 12:36 PM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] Re: Using PEC while guiding? Cem60

 

Bruce, can i have your permission to share this important information you posted on CN? So others can find it and stop regurgitating false info.

On Tuesday, February 27, 2018 at 6:32:35 PM UTC-5, Bruce Waddington wrote:

Hi Anthony.  I suspect the problem is not that the two don’t “work together”.  I think it’s more likely that the PEC is being done incorrectly in the first place or no longer reflects the behavior of the mount.  There really isn’t any sense of “working together” – the PE correction done in the mount controller happens first, long before PHD2 takes another exposure and measures the position of the guide star.  So when the PE curve is correctly programmed and applied, the mount simply looks to PHD2 like a mount that tracks better.

 

Unfortunately, there are various ways for people to get tripped up trying to apply a PE correction curve:

1.      The curve must be computed by a PEC application, it can’t be done effectively by hand while squinting through an eyepiece.  The application should measure the behavior over multiple worm cycles, then apply some statistical techniques to discard outliers (bad seeing, mount bumps, wind gusts) and correct for drift.

2.      PE correction in the mount can normally only deal with integer harmonics of the worm period, and trying to correct for other frequencies (over-programming the PEC) can makes things worse.

3.      Once the PE curve is uploaded to the mount, it’s important to measure the tracking again with PEC enabled.  In some cases (for reasons I’ve never learned), the curve may be inverted, meaning the tracking is actually worse than before.  In other cases, the mount vendor may have botched the implementation of PEC altogether.  So you’ll always want to have a “before” and “after” view of the RA tracking to be sure that you’ve actually improved things.