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  1. #1
    NorthernGator's Avatar
    NorthernGator is offline White Dwarf
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    Default My next steps to get better focus?

    HI all!

    I am just beginning to mess around with prime focus AP.

    I am having a hard time finding focus and looking for advice on my next steps. At the moment, I am not guiding, just trying to get the feel for short exposure first, but all my shots just don't have great focus. I would like to think it isn't my alignment, I do the Polar Alignment routine on my Celestron 8 inch SCT and do short exposures so star trails aren't an issue (hopefully). When I use the Polar Alignment routine on the CG5, I routinely get 0 0 0 RA, 0 0 0 Dec.

    The attached images are:

    -30 second, unguided exposures, ISO 1600, use shutter remote switch to trigger shutter so I don't touch the camera
    -CG5 mount
    -Canon Rebel T1i 500D camera
    -focus camera on Vega using Live View, then go to M57 or M13, whatever I am shooting
    -Celestron 8 inch SCT

    I have done some nice moon shots with prime focus, but I can see the moon on LiveView, I can't see anything on the screen for any Deep Sky object which is why I go to Vega first, I can see it in LiveView, then I magnify to 10X, focus and then Goto M57 or whatever to shoot the shot I want.

    Is my judgement of focus pretty poor?

    I can't use DSS to stack my shots because the stars are too out of focus for DSS. That's pretty humbling to get image scores of zero so they won't stack.

    Would a Bahtinov mask help? How can it help when I can't see any stars on the LCD screen on the camera when it is attached to the scope?

    Any ideas are appreciated.

    Attached Images Attached Images
    Celestron 8" SCT Advanced Series
    CG5 Mount
    Canon 550 D DSLR

  2. #2
    carch's Avatar
    carch is offline Bright Giants
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    Default Re: My next steps to get better focus?

    i have the same mount and do pretty much the same as you. but i use a sony NEX-5n camera. its live view has a magnifying mode making it alot easier to focus on a star

    and yes a mask should make it a perfect focus as long as its make right

  3. #3
    seigell's Avatar
    seigell is offline HYPER GIANT
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    Default Re: My next steps to get better focus?

    Yes. A Bahtinov mask is probably the best general purpose focusing aid available.
    The trick is that you DO NOT need to focus on the Star or DSO that you are going to image (which are usually rather dim), but rather to pick a bright star in the same area of the sky such as you have described (Vega or Deneb or ...)
    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
    CGEM (w HyperTune and ADM bling) / 2x CG5-AGT / Forest of Tripod legs / Star Adventurer / Orion EQ-G
    550D (Modded-G.Honis) / 60D / 400D / NexImage / NexGuide / Mini 50 SSAG / ST-8300C / ASI120MM-S / ASI1600MM-Cool
    Dark Skies in SW CO when I can get there, and badly light polluted backyard when I can't... (Currently Self-Exiled to Muggy Central Florida...)



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