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Thread: Still experiencing coma with Baader Planetarium Mark III coma corrector

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    Default Still experiencing coma with Baader Planetarium Mark III coma corrector



    M51 Final compressed.jpg

    This is a post processed image of M51 I took last night with my new "Orion 8" f3.9 Astrograph". Being a Newtonian scope I took this image with the Baader Planetarium Mark III coma corrector. Using a Bahtinov Mask I brought the brightest star close by "Alkaid" into view and focused my Nikon D3100 DSLR camera. Exposure time 2 hours of M51 made up of 12x 10min exposures. What I don't understand is why by my standards the stars look like garbage. I'm still fairly new to imaging or atleast experiencing total success in imaging. Is what I'm experiencing with my stars still coma or is this something different altogether. Used prime focus with DSLR for imaging. Any help is greatly appreciated. Wanting to know what is going wrong and what can I do to fix it. Thanks again -Stu

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    Default Re: Still experiencing coma with Baader Planetarium Mark III coma corrector

    Perhaps you can start by adding detail to the exact list of Optics Components connected between your Focuser and your D3100.

    As well, please confirm that your individual Exposures show the same "Bad Stars" issue as your final stacked Image.
    ES AR152 / ES 80ED Apo / Orion 8in F/3.9 / C9.25-SCT / C6-SCT / C10-NGT / AT6RC / ST-80 / AstroView 90 / Meade 6000 APO 115mm
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    Default Re: Still experiencing coma with Baader Planetarium Mark III coma corrector

    btw: That's worse Coma than I experience in my Orion 8" Astrograph without a Coma Corrector.
    ES AR152 / ES 80ED Apo / Orion 8in F/3.9 / C9.25-SCT / C6-SCT / C10-NGT / AT6RC / ST-80 / AstroView 90 / Meade 6000 APO 115mm
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    Default Re: Still experiencing coma with Baader Planetarium Mark III coma corrector

    You have one of the samples where the lens was inserted backwards. Just flip it. Check this post: Curved 3 vane spider, recommendations?
    Desert4wd likes this.
    Clear skies, Henk. Telescopes: Carbon fiber ES ED127CF, Zhumell Z12, Coulter Odyssey 10, AT6RC, Venture RX-7, Celestron Skymaster 20x80, Mounts and tripod: AVX, LXD55, Tiltall, Cameras: Canon (SX40, 450D, 350D, ELPH 100HS), Samsung NX100, DIY: Dob and camera barndoor trackers, afocal adapter, foldable Dob base with leveling feet, Az/Alt setting circles, Accessories: Counterweight bar attachment, Plossls, Barlows, Telrad, SSAG, laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: DSS, ImageMagick, PHD, Nebulosity, Photo Gallery, Gimp, CHDK

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    Default Re: Still experiencing coma with Baader Planetarium Mark III coma corrector

    DSC_0440.JPG

    Thanks for the speedy reply Seigell. I attached one of my subs and they all experience the same coma. Thankfully DSS is very forgiving and still stacked all 12 subs.

    As far as the exact list of optics I simply have the Baader Planetarium Mark III coma corrector, the rest is just adapters. Please see additional attached photo.

    Optics and Adapters.jpg

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    Default Re: Still experiencing coma with Baader Planetarium Mark III coma corrector

    Are you observing the correct spacing between the coma corrector and the camera's sensor? Coma correctors are extremely sensitive to the spacing. My Paracorr2, for example, requires 57mm spacing: 2mm for the adapter, and 55mm for the camera + t-ring. Your coma corrector will have a similar requirement, though the exact distance may be different. Generally, the tolerance is +/- 1 mm.

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    Default Re: Still experiencing coma with Baader Planetarium Mark III coma corrector

    Just a quick point to note is that your image is also out of focus a little. I have the Mk2 and didn't have any issues with it and my Canon cameras. The Canon has a mark on the body showing the plane of the chip. Not sure if the Nikon does or not. Double check the depth of the T-ring and the depth of the chip in the camera. Also if connecting it direct to the T-ring doesn't work then get a small spacer ring. Hope you get it figured out.

    Clear Skies

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    Mount:PMX+ Scope:FSQ106DX4Cameras:Atik383L+ mono with EFW2 filter wheel, Canon T2i modded, ZWO120mm-S for planetary, SBIG STi mono for guiding

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    Default Re: Still experiencing coma with Baader Planetarium Mark III coma corrector

    I posted a picture on my previous reply that showed the coma corrector and a few adapters. Per KeithBC suggestion I will be taking out the center two and just using the T adapter directly to the coma corrector and seeing if that will take care of the coma. I believe the spacing to the camera from the coma corrector is key. If this doesn't work I'll try CamelHat's suggestion of dismantling the coma corrector. I briefly did so and found I have two elements, wasn't sure to flip both or just one. Long story short the coma will now need a good cleaning. Thanks for the help guys, if it's clear skies tonight here in Wisconsin then we'll have an answer tomorrow.

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    Default Re: Still experiencing coma with Baader Planetarium Mark III coma corrector

    The way Chris' photos show it, he flipped the lens on the side that is facing inwards into the telescope tube (or, outward of the coma corrector if you will). In the original position the concave side was facing outward whereas the convex side should have been facing outward. Can you check if the convex part of the lens is facing outward of the coma corrector?

    Just to be sure, are we talking about the Baader MPCC Mark III? I was presuming we were, that's the one Chris and I have.

    EDIT: PS be careful when doing this, I can see how a lens could easily be scratched when using tools to remove the rings. I am contemplating doing it with mine to see the two lens elements, just not sure if the risk is worth it.
    Clear skies, Henk. Telescopes: Carbon fiber ES ED127CF, Zhumell Z12, Coulter Odyssey 10, AT6RC, Venture RX-7, Celestron Skymaster 20x80, Mounts and tripod: AVX, LXD55, Tiltall, Cameras: Canon (SX40, 450D, 350D, ELPH 100HS), Samsung NX100, DIY: Dob and camera barndoor trackers, afocal adapter, foldable Dob base with leveling feet, Az/Alt setting circles, Accessories: Counterweight bar attachment, Plossls, Barlows, Telrad, SSAG, laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: DSS, ImageMagick, PHD, Nebulosity, Photo Gallery, Gimp, CHDK

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    Default Re: Still experiencing coma with Baader Planetarium Mark III coma corrector

    Hello !
    Quote Originally Posted by caretaker View Post
    I dismantling the coma corrector. I briefly did so and found I have two elements, wasn't sure to flip both or just one. Long story short the coma will now need a good cleaning.
    As an optical dismantler ( ), with many bad experiences in my young years, put some marks on the side of each lens to dis-dismantle in exactly the same orientation (even rotation) (if Baader don't have put the lenses in the bad way !).
    The MPCC seems to be very sensitive regarding the spacing(look the user's manual).
    Clear sky and enjoy !
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