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  1. #1
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    Default CEM60 PEC & Guiding



    Hello everyone,

    I'm a new CEM60 owner and I really love it. I'm getting started in astrophotography and have captured about a half dozen nice images with it and an 8" RC scope.

    Last week I did periodic error correction (PEC) using PHD2 using instructions from iOptron tech support, and all seemed well. The process finished after 300 s, and the data integrity was good. I didn't actually enable it at that time, thinking that would be automatic.

    Then last night I enabled PEC with the hand controller just after starting up my mount at sunset. When I tried to do PHD2 calibration, though, I got "unexpected deviations" and RA step sizes were about 2x Dec steps when I looked at the resulting PHD2 cal graph. This was using a procedure I've used many times, which has always resulted in the RA & Dec steps being about the same. After four tries I disabled PEC and PHD2 was then able to cal as usual.

    After this, though, my guiding was poor (using the same PHD2 parameters which have performed well for several sessions). Dec seemed almost unresponsive, like the guide pulses were too narrow. RA seemed okay, but I wasn't paying much attention to it. This kept up for about an hour until the automatic mount meridian flip, when guiding performance was restored!

    This all looks like PEC is messing with my guide pulses. I didn't change either of them from the default 0.5, and checked a couple times during PHD2 cal to see if they'd changed. Has anyone experienced this? I'd sure like to use PEC and guiding!

    Thanks,
    Gerrit

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    Default Re: CEM60 PEC & Guiding

    Hi Gerrit,

    First off, welcome to the forum.

    After you start PEC then run the guiding assistant (GA) in PhD2 and see what results you get from that. It will make recommendations.

    Cheers,
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    Default Re: CEM60 PEC & Guiding

    Hi JT,

    Thanks for the reply. I did do GA, and it showed me my unguided Dec and RA and made recommendations for algorithm and backlash settings, as usual. I didn't see anything in there pertaining to this. Did I miss something?

    My guiding has been great up until last night after enabling PEC. My PHD2 settings were fine. Something in PEC made it so I couldn't calibrate PHD2 or guide properly, and my hunch is that my guide pulses were honked up by PEC somehow. (Guiding also started working again after my mount did its meridian flip.)

    Gerrit

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    Default Re: CEM60 PEC & Guiding

    Ok,

    One of our main contributors uses the CEM60 and it took him a while to get all the ducks in a row. Why don't you PM him and ask him the settings he uses in PHD2. It is member Hondo.

    Cheers,
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    Default Re: CEM60 PEC & Guiding

    Hi Gerrit and welcome to the forum.
    When I first got my mount and was looking at using PEC and autoguiding I came across a comment from iOptron support that said that the mount PEC and autoguiding are two separate control loops and they do not communicate with each other resulting in possible overcorrections. Based on that I never tried it but would be interested if someone else figured it out.
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    Default Re: CEM60 PEC & Guiding

    Thanks for the tips, JT and Alex. That's interesting about the PEC and autoguiding not playing well together. Theoretically there shouldn't be a problem, they should be independent, but I guess that's not the way it was implemented. Maybe I'll start hounding their support techs (who are very helpful, BTW). I have a note in to them right now, will let you know what they say.

    Gerrit

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    Default Re: CEM60 PEC & Guiding

    Hi Gerrit and welcome. CEM60 PEC and PHD2 do not play well with each other. There is a lengthy thread on the "other" forum about it. For my CEM60, I use the guiding assistant recommendations for Min Mo but I use low aggressiveness settings on RA and Dec. The Snip attached is a typical session with the CEM60.

    Attachment 185737
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    Default Re: CEM60 PEC & Guiding

    Thanks, Hondo, that's great information and corroborates Alex. Before shooting myself in the foot with PEC last night I was getting good results with the PHD2 Lowpass algorithms on RA and Dec. The CEM60 has pretty low Dec backlash, so I found I didn't need to use the Resist Switch algorithm. I usually get about 0.4 arc-s long-term RMS error on both RA & Dec, with peaks to 1 occasionally. I see very little wind here, so that helps. That's well below my typical seeing, so I'm happy with it.

    Settings for PHD2 vary a lot, depending on your OTA focal length and the angular sampling relationship between your main tube and your guide cam. It seems like everyone has to go through the pain of tweaking their own systems.

    Gerrit

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    Default Re: CEM60 PEC & Guiding

    Based on my research at various forums, no one seems to be able to use PEC with guiding on the CEM60. iOptron tech support just replied, "We do not recommend running PEC while guiding since they are two separate feedback loops and do not talk each other."

    I think this is nonsense. The reason you record a cycle of PE is so you can simply play it back open-loop during operation. There should be no feedback loop involved in in-mount PEC, and PEC and guiding should be able to coexist fine.

    I registered this as a bug report to iOptron. If you agree, consider sending a note to support@ioptron.com .

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    Default Re: CEM60 PEC & Guiding

    Quote Originally Posted by TinySpeck View Post
    Based on my research at various forums, no one seems to be able to use PEC with guiding on the CEM60. iOptron tech support just replied, "We do not recommend running PEC while guiding since they are two separate feedback loops and do not talk each other."

    I think this is nonsense. The reason you record a cycle of PE is so you can simply play it back open-loop during operation. There should be no feedback loop involved in in-mount PEC, and PEC and guiding should be able to coexist fine.

    I registered this as a bug report to iOptron. If you agree, consider sending a note to support@ioptron.com .
    My own experience is similar that PEC and guiding do not operate well together on my CEM60.
    I also agree it is a nonsense, there is no need for the two mechanisms to talk to each other, and just points to a poor firmware implementation. Certainly many other mount manufacturers manage to implement it.
    Good luck registering your bug report, I got nowhere other than the standard reply you've already received. I certainly would like to use PEC and guiding together but I gave up and just run guiding on its own. It works well enough once dialled in and I now guide to 0.35" on average.
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