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  1. #1's Avatar Guest

    Default planetary eyepiece for skyquest xt 4.5

    Hi everyone,
    What is the maximum useful magnification for the skyquest(dobsonian)
    4.5 inch telescope, for viewing planets and the moon?
    What is a good quality eyepiece you would recommend?
    [Would it be useful to buy a wide field eye piece with focal length in
    the range - 4 to 6 mm?]

  2. #2
    Starlord's Avatar
    Starlord Guest

    Default planetary eyepiece for skyquest xt 4.5

    I've used everything from a 4.8mm to a 17mm on my Stargazer Steve 4.25inch
    F9 Dob.

    There are those who believe that life here, began out there, far across the
    universe, with tribes of humans, who may have been the forefathers of the
    Egyptians, or the Toltechs, or the Mayans. Some believe that they may yet be
    brothers of man, who even now fight to survive, somewhere beyond the

    The Lone Sidewalk Astronomer of Rosamond
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  3. #3
    Joe S.'s Avatar
    Joe S. Guest

    Default planetary eyepiece for skyquest xt 4.5

    <> wrote in message

    Rule of thumb for maximum magnification is 50 multiplied by the aperture in
    inches. So, in the case of the 4.5, the result is 4.5 x 50 = 225X --
    maximum magnification is 225X.

    XT-4.5 focal length is 910mm. Magnification is focal length of the scope
    divided by focal length of the eyepiece. Thus, a 4mm eyepiece would yield:
    910 mm divided by 4mm = 227X. A 4mm eyepiece will get you to maximum
    magnification for this scope.

    Then there is the consideration for exit pupil size and eye relief, none of
    which I understand but I'm certain there are lots of wise people here who
    will tell you about those two aspects.

    Practically speaking, you are not likely to be happy running the scope up to
    max magnification because the max mag you can use is really limited by
    seeing conditions -- atmospheric conditions, light pollution, and the like.
    A 5mm eyepiece will give you 182X, which will show you a lot of planetary
    detail while staying below max mag.

    I have an XT-12, 1500mm focal length, theoretical max mag is 600X. For
    planets, I use a 7mm Nagler (214X), a 10mm Radian (150X), and a 5mm
    University Optics orthoscopic (300X). Most nights, the 7mm at 214X is the
    best I can do what with light pollution and atmospherics. Occasionally I
    can use a 3.7mm Orion ED eypiece at 405X, but those nights are rare.

    Another factor is movement and field of view. As mag goes up, FOV becomes
    smaller. At 300X in my scope, a planet (or any other object for that
    matter) moves across the FOV rather quickly and I find myself spending more
    time moving the scope than observing.

    A lot of folks prefer orthoscopic eyepieces for planetery work because they
    have fewer glass elements to interfere with the light path, thereby
    supposedly revealing more planetary detail. You might look at University
    Optics orthos -- good eyepieces, modest prices -- but orthos have very
    little eye relief.

    Here is a discussion of eyepieces that uses only TeleVue eyepieces:

    Another option is to get yourself a good 2X Barlow. I see in the Orion
    catalog that the XT-4.5 came with two eyepieces that yield 36X and 91X.
    With a 2X Barlow, you'll now have 36X, 72X, 91X, and 182X. Try that, see
    what 182X does for you -- then, you would have an idea of what higher mags
    look like and you can decide if you want another eyepiece or just stick with
    the existing eyepieces and the Barlow.

  4. #4
    Joe S.'s Avatar
    Joe S. Guest

    Default planetary eyepiece for skyquest xt 4.5

    <> wrote in message

    Check out this discussion of eyepieces and selecting eyepieces for various

  5. #5
    Joe S.'s Avatar
    Joe S. Guest

    Default planetary eyepiece for skyquest xt 4.5

    <> wrote in message

    And, as if you will not get enough advice, here is another link:

  6. #6
    John Carruthers's Avatar
    John Carruthers Guest

    Default planetary eyepiece for skyquest xt 4.5 wrote:

    Value for money; a 5 or 6mm orthoscopic, not a huge field but sharp.
    Maybe a Burgess/TMB planetary, wider field,I use a 6mm.
    Cash no object ? a 5mm monocentric, I want one :-)

  7. #7
    W. H. Greer's Avatar
    W. H. Greer Guest

    Default planetary eyepiece for skyquest xt 4.5

    On 11 Dec 2006 19:09:12 -0800, wrote:

    Hi Marvin,
    It's easier to use wide-field eyepieces for high magnifications with a
    Dobsonian. The wider field makes it easier to keep the object in the
    field of view, even if (as is likely) the image quality deteriorates
    as the object approaches the field edge.

    The maximum useful magnification depends on the quality of the optics,
    the accuracy of the scope's collimation, and the seeing conditions
    (among other things). Some 4.5 inch scopes can handle 250x. Others
    might top off at 100x or even less!

    *If* the telescope provides sharp, crisp planetary images with the
    highest power (10mm) eyepiece it's supplied with, then I would suggest
    getting a 6mm wide-field eyepiece (about 150x for the 4.5 inch
    Skyquest). You could later go up a bit higher *if* the image remains
    sharp and crisp. On the other hand, if planetary images are "fuzzy"
    with the 10mm eyepiece, then there's little point in purchasing a
    shorter focal length eyepiece.

    In a "best case" scenerio, when *everything* is perfect, a high
    quality 4.5 inch scope would be able to handle a maximum magnification
    in the neighborhood of 270x. Would *any* 4.5 inch Skyquest qualify at
    such a magnification? I don't know!

    In addition to the factors mentioned above, different individuals have
    different tolerances and preferences concerning maximum useful
    magnification. There's also the mount to consider. Your maximum
    useful magnification will not be the same for all objects, nor for the
    same object on different nights. In the end, it's your job and duty
    to find the right magnification for each task. In some aspects (such
    as selecting the right magnification) amateur astronomy is an
    experimental science.

    Experiment, Observe, and Enjoy!
    Celestial Journeys

  8. #8
    Dennis Woos's Avatar
    Dennis Woos Guest

    Default planetary eyepiece for skyquest xt 4.5

    <> wrote in message

    The best thing you can do is to connect with the folks in your local astro
    club, and attend events where you will be able to test out more eyepieces
    than you can shake a stick at. That said, I really like our 6mm Burgess
    Planetary garage-sale eyepiece - $50. Don't think that spending a lot of
    money is going to make a very big difference in your views - it won't. What
    big money buys you over a good Plossl is wide-field and eye-relief, and the
    Burgess gives you both of these benefits at a Plossl price. Only you can
    decide if your scope and seeing conditions make a 6mm worth-while.




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