Dithering without guiding

Discussion in 'Image Capture' started by Herbert Sauber, Apr 4, 2017.

  1. Herbert Sauber

    Herbert Sauber Cyanogen Customer

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    Location:
    Mittenwalde, Germany
    Hello,
    I use a 10Micron GM2000 controlled my MaxIm DL 6.13. Since tracking of the GM2000 is so precise, no guiding is necessary when capturing images up to ten minutes. Dithering, however, is required to obtain high quality images. So far I did not succeed with MaxIm DL 6.13 to dither while not guiding. When I choose the option "Dither Via Mount" the mount moves in X-direction far too much as dithering is supposed to do. After several frames the target is moved out of the frame.
    Some discussions in the 10Micron forum suggest other software, SGP for example, instead of MaxIm. Does that really mean that it is not possible with MaxIm?

    Any help would be highly appreciated.

    Herbert, Germany
     
  2. Doug

    Doug Staff Member

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    The feature definitely works; I have used it on many occasions.

    What telescope mount are you using? Some mounts are not capable of small distance moves via slew command.
     
  3. Herbert Sauber

    Herbert Sauber Cyanogen Customer

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    Location:
    Mittenwalde, Germany
    I have a GM2000 HPS II Ultraport and use the 10Micron driver for Ascom. For imaging I use a Takahashi FSQ-106 and a SBIG ST-10. The whole equipment ist placed in the namibian mountains and I make at the moment the first steps to control it remotely from Germany.
     
  4. Doug

    Doug Staff Member

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    I'm not familiar with that mount. Try experimenting with, say, a series of 2 arc-second slews (via Telescope tab) in the four different directions. If you can slew 2 arc-seconds reliably in any direction then you should be able to dither. If you can't then that's the problem.
     
  5. Herbert Sauber

    Herbert Sauber Cyanogen Customer

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    Thanks Doug. I downloaded a recent driver for the mount and switched to coordinates JNow on both the mount and MaxIm. Now, slewing the mount by small amounts works and a first series of images was dithered correctly. Whatever the reason is, the new driver or coherent coordinates. There is only one item which worries me: Slewing in declination works perfectly for smaller or bigger amounts. Slewing in right ascension, however, behaves strangely: slewing by 1 degree changes right ascension by 6'20". I supposed right ascension to change by 4'. I hope there is no flaw in my calculation! Equivalent differences occur when I slew by 1' or 1".
    Is there an explanation?

    Best regards
    Herbert
     
  6. Doug

    Doug Staff Member

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    That sounds off. I don't have an explanation. Use the ASCOM Pipe tool to monitor the messages going to/from the mount. That will tell you if the problem is in MaxIm DL or in the mount software/firmware. (I'm betting on mount.)

    In any case, it's a small amount and probably immaterial for dithering. Just set the dither distance appropriately.
     
  7. Herbert Sauber

    Herbert Sauber Cyanogen Customer

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    Location:
    Mittenwalde, Germany
    The pipe tool is something I still have to get familiar with. But I tried slewing with an Astro-Physics mount Mach1 and there again, slewing in right ascension depends on declination δ. Only on the celestial equator a slew of 1° moves the scope by 4' in right ascension, as it should be. In other positions it is more. It seems that a factor of cos δ is missing in the pulse length sent to the mount.
     
  8. Doug

    Doug Staff Member

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    Ah, well, it's a distance in Right Ascension, not a distance in linear distance. There's your cosine term right there.
     

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