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Thread: Flexure/stiction - or something else

  1. #1
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    Default Flexure/stiction - or something else



    Here is one of the bad frames from my recent attempt at M51. The star trail is in line with the RA axis, so it is trailing in the Dec direction, if I am interpreting this right. Further I as assuming there is an instant jump in the star position and PHD2 is moving it's maximum amount over several steps to recover. This doesn't make any sense to me as I wouldn't expect any trailing in this direction along a line of constant RA, I would expect trailing along a line of constant DEC.

    I just don't get what is happening here at all. As such I'm not sure how to fix it. If anyone can explain what is happening I would love to hear from you!

    full frame
    M51 WHIRLPOOL_LIGHT_180s_1600iso_+64f_00706stdev_20160609-23h59m21s681ms.jpg

    crop
    M51 WHIRLPOOL_LIGHT_180s_1600iso_+64f_00706stdev_20160609-23h59m21s681ms_crop.jpg

    BTW, do you like my light pollution? This are two minute frames at ISO 1600. (I meant to do 800, but I guess I set it wrong in BYEOS.)

    Thanks,
    Bob
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    Sundedo's Avatar
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    Default Re: Flexure/stiction - or something else

    So it wasn't in all your frames?

    And we need to get you a LP filter
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    Default Re: Flexure/stiction - or something else

    It wasn't in all the frames. 40% were perfect, about 20% had slightly oval stars, and 20% had this larger effect. The others had trees (oops).

    I've tried an LP filter in the past, but I have mixed feelings about them and what they do to the color balance. I am able to deal with it in post fairly well, I think. The jury is still out on it for the long run. More time on target will also be a help, if I every get the guiding straightened out.

    8 stacked lights 3 - levels curves saturation brightness.jpg 8 stacked lights 3 - levels curves saturation brightness cropped.jpg

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    Default Re: Flexure/stiction - or something else

    My opinion is its seeing related. Take that with some salt as I'm still sorting out my guiding issues so am far from an expert.

    Can you post your guide log?
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    Default Re: Flexure/stiction - or something else

    If you have any coiled cords, check them first... It looks to me, (without seeing your PHD graph), that it sticks, slides a bit and then releases...
    You get some good, some so so and some terrible... Coiled and flat cables are the worst for sticking and messing up guiding.
    (Nice start on the Whirlpool, BTW... )
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    Default Re: Flexure/stiction - or something else

    I can post my guide log, now that I found it, then I zipped it up. I guess now I'll have to figure out how to read it One thing I do recall after looking at the log was the exposures were actually three minutes, not two. I am seeing some star lost drops in there - for low SNR (I still am not happy with my camera setup) and mass changes?

    PHD2_GuideLog_2016-06-09_232655.zip

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    Default Re: Flexure/stiction - or something else

    Your dither is off the charts crazy high! Also did not see any real 'cool down' from it either.

    it might just be it is struggeling to recover from the dithers.

    Oh yea the first calibration was not great.

    One more thing. I noted you were using 'on camera' assuming an ST4 connection, how are you sending dither commands?
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    Default Re: Flexure/stiction - or something else

    Quote Originally Posted by jimminCT View Post
    If you have any coiled cords, check them first... It looks to me, (without seeing your PHD graph), that it sticks, slides a bit and then releases...
    You get some good, some so so and some terrible... Coiled and flat cables are the worst for sticking and messing up guiding.
    (Nice start on the Whirlpool, BTW... )
    No coiled cables, the one that runs from the starshoot autoguider camera to the mount autoguide port is flat. I have setup for ASCOM control in the past (mostly to upgrade the hand controller firmware, and I am thinking of going that route for autoguiding as well, which will reduce the number of cables coming off the OTA by one - and eliminate the flat cable entirely. Thanks for the suggestion.

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    Default Re: Flexure/stiction - or something else

    Quote Originally Posted by bobharmony View Post
    I can post my guide log, now that I found it, then I zipped it up. I guess now I'll have to figure out how to read it One thing I do recall after looking at the log was the exposures were actually three minutes, not two. I am seeing some star lost drops in there - for low SNR (I still am not happy with my camera setup) and mass changes?

    PHD2_GuideLog_2016-06-09_232655.zip

    Bob
    This is what I use to read my logs

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    Default Re: Flexure/stiction - or something else

    There was no wind present at all when you were imaging? It looks like it was happening right in mid exposure.
    My eyes
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