Using PEC on the mount with PHD2

[Tom van Peer]

Hi All,

I am working to set up PEC on my iOptron CEM26 and would like some help on how to combine this with PHD2. I can train PEC by sending guide pulses to the mount, so my initial idea is to calibrate PHD2, let the PHD2 guide the mount and then train PEC. Then switch PEC on, run GA and I should be done. But I am sure I am missing some steps here. One question I have for sure is what guiding algorithm to use for RA if PEC is on? Is PPEC the best choice, even when PEC is already in place? Would it make sense to run GA as well before training PEC? Any help is appreciated. Thanks.

[Brian Valente]

Hi Tom

Before you go too far on this, there has been some varied responses regarding PEC with IOptron mounts and guiding

https://www.cloudynights.com/forums/topic/789440-pec-and-guiding-interaction-theoretical-question/

you should confirm with IOptron and/or other IOptron users if IOptron's PEC implementation and guiding work well together

However, assuming they do:

>>> am working to set up PEC on my iOptron CEM26 and would like some help on how to combine this with PHD2. I can train PEC by sending guide pulses to the mount, so my initial idea is to calibrate PHD2, let the PHD2 guide the mount and then train PEC.

that's fine and pretty typical. You may want to consult IOptron PEC software specifics regarding ability to set an offset the training. Remember the guidepulses happen after the error, so there will be some offset to the PE data that may be correctable via IOptron PEC software.

>>>>Then switch PEC on, run GA and I should be done. But I am sure I am missing some steps here. 

not really. You should do the baseline, not just the GA (see below)

>>>One question I have for sure is what guiding algorithm to use for RA if PEC is on? Is PPEC the best choice, even when PEC is already in place? Would it make sense to run GA as well before training PEC?

It depends on what the residual error looks like. your best bet is to do a baseline guidelog (see attached PDF) before PEC training and then after. That way you'll have a clear idea of how effective PEC is, and what is left to guide out. PPEC is often a complement to mount-based PEC.

On Fri, Feb 6, 2026 at 12:04 PM Tom van Peer <tvan...@gmail.com> wrote:

Hi All,

I am working to set up PEC on my iOptron CEM26 and would like some help on how to combine this with PHD2. I can train PEC by sending guide pulses to the mount, so my initial idea is to calibrate PHD2, let the PHD2 guide the mount and then train PEC. Then switch PEC on, run GA and I should be done. But I am sure I am missing some steps here. One question I have for sure is what guiding algorithm to use for RA if PEC is on? Is PPEC the best choice, even when PEC is already in place? Would it make sense to run GA as well before training PEC? Any help is appreciated. Thanks.

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Brian Valente

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[Tom van Peer]

Hi Brian,

Thanks for your comments and suggestions! Answers and additional question in-line...

On Friday, 6 February 2026 at 21:48:40 UTC+1 bval...@gmail.com wrote:

Hi Tom

Before you go too far on this, there has been some varied responses regarding PEC with IOptron mounts and guiding

https://www.cloudynights.com/forums/topic/789440-pec-and-guiding-interaction-theoretical-question/

you should confirm with IOptron and/or other IOptron users if IOptron's PEC implementation and guiding work well together

I am getting different signals. Apparently in the past PEC did not work well with PHD2, but I have seen at least one example of someone getting it to work with their iOptron mount on CN. That thread you mentioned is also quite a mixed bag of opinions, varying from 'Personally, I don't see the point of PEC with guiding.' to 'Pec with guiding is the gold standard if you don't have encoders.'. But apart from opinions it contains quite some usable information as well. 

 

However, assuming they do:

>>> am working to set up PEC on my iOptron CEM26 and would like some help on how to combine this with PHD2. I can train PEC by sending guide pulses to the mount, so my initial idea is to calibrate PHD2, let the PHD2 guide the mount and then train PEC.

that's fine and pretty typical. You may want to consult IOptron PEC software specifics regarding ability to set an offset the training. Remember the guidepulses happen after the error, so there will be some offset to the PE data that may be correctable via IOptron PEC software.

Ioptron PEC (for the CEM26) does not let you set any options, it records for one worm cycle, checks the integrity and that's it. Someone on CN ran PPEC for several worm cycles and then started PEC recording. In that way you would have more predictive pulses going into the training instead of 'after the error'. Does that make sense in your opinion ?

 

>>>>Then switch PEC on, run GA and I should be done. But I am sure I am missing some steps here. 

not really. You should do the baseline, not just the GA (see below)

As I am also expecting a new guide camera and having my mount serviced, I was planning to indeed do the whole baseline. 

[Brian Valente]

Tom

>>>I am getting different signals.

you aren't the first. I would go with whatever IOptron officially says, but you will probably end up having to experiment.

>>>Someone on CN ran PPEC for several worm cycles and then started PEC recording. In that way you would have more predictive pulses going into the training instead of 'after the error'.

it's a step in the right direction, but remember PPEC has both a predictive and a reactive part to the algorithm, so it's not going to completely resolve this. It's probably the best place to start. I would also make sure you set the period to your known primary period and disable auto adjust.

Let us know how it goes and what you find. Maybe there will be a more definitive answer for other IOptron owners

Brian

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/4bef3ce5-dd54-4e1a-8063-fcd48177f8b6n%40googlegroups.com.

[Tom van Peer]

Brian,

Since it is still cloudy here and I haven't found more specific on iOptron PEC (other than how PemPRO does it), I had some time to do some more (over)thinking

and here is the idea. Let PPEC train for 5 or 6 worm cycles if that can be set (expert setting?), then set it to 100% predictive gain, 0% reactive gain, and start PEC. And as you suggested, set the period to the CEM26 worm period. Should I set auto adjust if I can run training for more than 2 periods? Does all this make some sense?

Tom 

[Brian Valente]

Tom

please send this question to the group and I can answer there. We try to keep everything public to help others

Thanks

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/c73f4dd1-80ba-4b62-94cf-c2d062a6a950n%40googlegroups.com.

[Brian Valente]

you only need about 3 cycles before PPEC fully kicks in. I would just leave the defaults for PPEC. Your assumption is that PPEC completely corrects for PE, which isn't accurate. it can only target a single frequency, whereas your mount's PE is often multi-period, with various harmonics. So there's value in having both.

Don't use the auto adjust, that's really if you don't know what the period is. Your mount's primary PE is not going to change.

And yes, don't overthink it too much. experimentation here is key

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/c73f4dd1-80ba-4b62-94cf-c2d062a6a950n%40googlegroups.com.

[Brian Valente]

>>>please send this question to the group and I can answer there. We try to keep everything public to help others

EDIT: well i blew that one, so please ignore this comment