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  1. #1
    Jack's Avatar
    Jack Guest

    Default CCD to match Celestron 11" SCT?



    Good day

    I am interested in getting a Celestron 11" SCT for minor planet
    astrometry but need to decide on a CCD camera to match the telescope.

    From the Minor Planet Centre, I got the following recommendation:

    "You will need to know the focal length of your telescope and the
    physical size of your CCD's pixels to calculate the pixel scale.
    Your setup should be such that the pixel scale is no greater than 2"/
    pixel (preferably) or 3"/pixel (at worst).

    In practice, your optimal pixel scale is something that you will have
    to determine for yourself, taking into consideration the capabilities
    of your telescope and CCD and the seeing at your site.
    If your pixel scale is much larger than the values quoted above, then
    the quality of the astrometry will suffer.
    If your pixel scale is too low for your local setup, then the signal-
    to-noise of the images may be low as each image is spread over a large
    number of pixels."

    I have found a calculator at

    http://www.starlightccd.com/faq/ccdcalc.htm

    to calculate the pixel scale for their products but what is the actual
    formula?

    The 11" Celestron has an aperture of 280 mm and a Focal Length of 2800
    mm.

    Which CCD cameras would you recommend? Which ones should I avoid? My
    budget is limited to $1500 but I could push it to $2000 if I really
    have to.

    Thanks
    Jack

  2. #2
    Chris L Peterson's Avatar
    Chris L Peterson Guest

    Default CCD to match Celestron 11" SCT?

    On Wed, 10 Jun 2009 06:36:27 -0700 (PDT), Jack
    <newsgroupreader1@gmail.com> wrote:


    A = 206265 * d / F

    where
    A is the pixel scale in arcseconds;
    d is the pixel pitch;
    F is the telescope focal length (in the same units as d)

    (206265 is the number of arcseconds per radian)


    Thus, 2 arcsec = 206265 * d / 2800.

    d = 27 um.

    In other words, this telescope requires a large pixel camera to get your
    desired scale of 2"/pixel. With typical science cameras having pixels
    that are 9 um, you will be rather oversampled. That's actually not a big
    problem for most astrometry, but you could easily reduce your focal
    length. I'd look at using a 0.6x reducer (which will also produce a
    flatter field). That will give you

    A = 206265 * 0.009mm / 1680mm = 1.1 arcsec/pixel.

    That's a very nice imaging scale, and depending on your target you can
    opt to bin 2x2 to get 2.2 arcsec/pixel. Of course, it also means you
    have a larger FOV than using the native focal length of your scope.


    That is a very limiting budget for a good science camera. Avoid any
    camera with a color sensor, avoid any camera that isn't cooled, avoid
    any camera that can't take long exposures, avoid any camera without a
    mechanical shutter. Cameras with full frame sensors will generally give
    better results than cameras with interline sensors, although you can get
    good results with either. Sensors with deep pixels (high dynamic range)
    are often useful for astrometry and photometry, since this allows you to
    have fewer saturated reference stars to compare with your (usually dim)
    target.

    Take a look at the SBIG ST402, or the ST7 if you need self guiding.
    These are very good cameras for what you're interested in. The only down
    side is that the sensors are rather small, which means you will have
    fewer reference objects in the field than you might want.
    _________________________________________________

    Chris L Peterson
    Cloudbait Observatory
    http://www.cloudbait.com

  3. #3
    Jack's Avatar
    Jack Guest

    Default CCD to match Celestron 11" SCT?

    > That is a very limiting budget for a good science camera.


    Mr. Peterson, thank you very much for your advice.

    For a total of $3000, which SBIG CCD would you recommend as a third
    option using the setup as described and with a Focal Reducer?

  4. #4
    *skyguy*'s Avatar
    *skyguy* Guest

    Default CCD to match Celestron 11" SCT?

    Hi Jack,

    For a number of years, I've used an SBIG ST9-E camera on a Meade 12"
    LX200 at F6.3, for minor planet astrometry. It's an almost perfect
    match, with the camera's 20-micron pixels giving an image scale of
    2.18 arc-seconds/pixel. It has a very high "Full Well Capacity" of
    150,000 e-, which "cuts down" on the number of saturated stars per
    image. You can find a used parallel port model for about $1,000 on the
    used astronomy equipment sites. Also, contrary to popular belief, the
    camera is capable of taking beautiful deep-sky images ... using the
    proper image processing techniques. Check-out this image of NGC 4565 I
    took with this camera a few weeks ago:

    http://www.geocities.com/jdilapo/NGC...5B25_final.jpg

    Good Luck,

    Jim

    On Jun 10, 9:36 am, Jack <newsgroupread...@gmail.com> wrote:


 

 

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