PHD2 and mount PEC

[Gianluca Rossi]

I have found confusing opinions about the opportunity to activate PEC in the mount while guiding with PHD2. Is it worth trying it? Or is it prefearable to run the predictive pec algorithm of PHD2? In the case of activating mount PEC which algorithm has to be used in PHD2?

Thank you very much

Gianluca

[Jens Scheidtmann]

Dear Gianluca, 

It believe it is hard to give general recommendations on that, as their use and the gain you can get depends on the mechanical imperfections the mount has. Sometimes it may also be driver dependent.

For example in my case, an AZ-EQ6 with a particularly bad worm gear performance of 50“ peak-to-peak and an additional period due to transmission belts, acceptable performance can be achieved by running both PPEC (periodic PEC, stored in the mount) and predictive PEC (in PHD2, in software) in parallel. So in my case there is positive experience running both.

Which of these technologies you use, should IMHO depend on the performance you want to achieve. So, if you‘re satisfied with your imaging system and it yields small round stars, and you‘re achieving it with-out these technologies, why bother? It boils down to: how do you define „good performance“ of your imaging system?

Best regards, Jens

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[Gianluca Rossi]

Well I think it is worth trying after all. My problem is that I cannot get consistent results with my eqm35 pro. Sometimes I get a RMS of about 0.5 arcsec while other times I get much worse results such as 1.7 arcsec. The latter delivers elongated stars. I am trying to improve mechanically the RA drive but perhaps PEC can offer some help. My question about using PEC comes after reading a lot of reports saying that with guiding one should disable PEC. I have now learned that PHD2 can handle native PEC so I will definitely give it a try to see if I can get some improvement.

Gianluca

[Brian Valente]

Hi Gianluca

In general terms, you want to use every tool available to you to improve tracking, so generally yes you want to use mount-based periodic error correction PEC) in addition to guiding. *Any* properly configured guiding will likely help. 

The confusion may be where some mounts have a mount-based PEC that does not play well with guiding. If you are one of the unlucky few in this circumstance, you are somewhat forced to choose between them. I don't recall the specifics here, but I believe there are some ioptron and/or mounts using EQMod that don't play well here. I may be mistaken and/or there are other mounts with the same issue. You will need to figure the answer out in a mount-specific forum, or via the manufacturer.

As a separate point, If you have a mount that plays well with guiding, and after mount-based PEC still has a large periodic error (it may not be the primary period, but is still regularly occuring, such as a 2x or 3x period), you can  also use the predictive PEC (PPEC) algorithm in PHD to target that particular period. This one-two punch is a common strategy and can be effective

hth

Brian

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Brian Valente

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[Gianluca Rossi]

Hello Brian,

I do not use EQmod as I  actually prefer GSServer which to me is by far better. I will ask the manufacturer about the possibility to use mount-based PEC with guiding but I think it may be worth a try. One recommendation I could read is to instruct mount-based PEC at every session as it is likely not to work from one session to another but I may be mistaken. Do you have any particular opinion about this advice?

Gianluca

[Brian Valente]

What mount do you have?

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[Gianluca Rossi]

I have both an Heq5 Pro and an EQM35 Pro. I have asked Skywatcher to let me know if PEC works with guiding but they say that the autoguider takes over.

[Brian Valente]

>>> I have asked Skywatcher to let me know if PEC works with guiding but they say that the autoguider takes over.

sounds like you have your (unfortunate) answer, that Skywatcher's internal PEC does not play well with autoguiding. 

So I would opt for guiding + using PPEC algorithm for RA

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