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  1. #1
    W. eWatson's Avatar
    W. eWatson Guest

    Default Image Seen with a Newtonian Reflector?



    I don't own a Newtonian, but I'm curious whether the image is mirror,
    interted (upside-down) or something else. Googling for these attributes
    produces vague descriptions that suggest the image cannot be made erect.
    That seems odd. If that's the case, I would think there's some common
    accessories that are just not right for producing an erect image for it,
    rather than it being impossible. The only bizarre image I can think of not
    only is it inverted, but somehow left and right get swapped.

  2. #2
    AstroSketcher@gmail.com's Avatar
    AstroSketcher@gmail.com Guest

    Default Image Seen with a Newtonian Reflector?

    On Jul 10, 6:11 pm, "W. eWatson" <notval...@sbcglobal.net> wrote:


    The image is more or less upside down. The exact amount by which the
    image is rotated depends upon the placement or orientation of the
    focuser. IOW, the image is *not* mirror-reversed. It's a correct,
    but rotated image. For astronomy it works out very nicely.

    Bill Greer
    To sketch is to see.
    http://cejour.blogspot.com
    http://www.rangeweb.net/~sketcher

  3. #3
    wrhamblen@comcast.net's Avatar
    wrhamblen@comcast.net Guest

    Default Image Seen with a Newtonian Reflector?

    On 2008-07-11, W. eWatson <notvalid2@sbcglobal.net> wrote:

    The image in a newtonian is not a mirror image because the
    telescope has an even number of reflections. One reflection
    reverses the image, like looking in the bathroom mirror, but
    the second reflection flips it again and the result is not
    reversed. The image does appear rotated compared to the naked
    eye view, depending on the angle you look into the eyepiece.
    The problem with using an erecting prism in a newtonian is
    that an erecting prism moves the eyepiece 2 or 3 inches out
    from the focuser and you would need to crank the focuser in the
    same 2 or 3 inches to focus. Most newtonians don't have that
    much inward movement from the normal focus position.

    Bud


  4. #4
    W. eWatson's Avatar
    W. eWatson Guest

    Default Image Seen with a Newtonian Reflector?

    AstroSketcher@gmail.com wrote:

    What sort of sky map would one use then to work with a Newtonian reflector?
    If I'm using a schmidt-cass with an eyepiece but no diagonal, then I'd take
    a typical star map and turn it upside down (south at top and east to the
    left). If I'm using it with a diagonal, then I need a map that interchanges
    right with left.

  5. #5
    W. eWatson's Avatar
    W. eWatson Guest

    Default Image Seen with a Newtonian Reflector?

    AstroSketcher@gmail.com wrote:


    If the image is only rotated, then I don't see a problem with using a
    standard north is up and east is right star map. Likewise, I do not see why
    various, perhaps mostly commercial, just don't come right out and say you
    may be twisting your head and body greatly to orient the view upright;
    therefore, a Newtonian should not be used for terrestrial viewing.

    If it's not just simply rotated, then what sort of sky map would one use
    then to work with a Newtonian reflector? If I'm using a schmidt-cass with an
    eyepiece but no diagonal, then I'd take a typical star map and turn it
    upside down (south at top and east to the left). If I'm using it with a
    diagonal, then I need a map that interchanges right with left.

  6. #6
    W. eWatson's Avatar
    W. eWatson Guest

    Default Image Seen with a Newtonian Reflector?

    wrhamblen@comcast.net wrote:
    See my response to Autosketcher, but from this, and his similar remark
    that's a matter of rotation, that eyepiece viewing really doesn't doing
    anything odd. However, one may have to rotate their head and body to orient
    the view to an erect image, that is north is up and east is right.

  7. #7
    W. eWatson's Avatar
    W. eWatson Guest

    Default Image Seen with a Newtonian Reflector?

    Skip this one. I sent it before I was ready. See the next one at 57 minutes.

  8. #8
    wrhamblen@comcast.net's Avatar
    wrhamblen@comcast.net Guest

    Default Image Seen with a Newtonian Reflector?

    On 2008-07-11, W. eWatson <notvalid2@sbcglobal.net> wrote:


    SkyAtlas 2000 is popular. The laminated editions hold up better in the dew,
    but are heavy.

    Bud


  9. #9
    W. eWatson's Avatar
    W. eWatson Guest

    Default Image Seen with a Newtonian Reflector?

    wrhamblen@comcast.net wrote:
    I was thinking of orientation. Mirror, inverted, ...

  10. #10
    Paul Schlyter's Avatar
    Paul Schlyter Guest

    Default Image Seen with a Newtonian Reflector?

    In article <Cxxdk.5856$vn7.2897@flpi147.ffdc.sbc.com>,
    W. eWatson <notvalid2@sbcglobal.net> wrote:

    The orientation of the image in a Newtonian telescope is dependent on the
    rotation of the tube: is the eyepiece on top of the telescope tube, or on
    one side of the tube?

    First, the image is not a mirror image, because there's an even number of
    mirrors in a Newtonian: the primary mirror and the secondary mirror.
    The same goes for a Cassegrain telescope btw. Only if the telescope has
    an odd number of mirrors (such as in a Herschelian telescope with only
    the primary mirror, or as in a Nasmyth/Coude telescope with a primary
    mirror, a secondary mirror, and a tertiary mirror) will the image be a
    mirror image.

    Now back to the normal reflector: in a Cassegrain telescope the image
    is upside-down just like in a refractor, and it's the same with a Newtonian
    telescope if the eyepiece is on top of the telescope tube. But if the
    eyepiece is on the side of the Newtonian telescope tube, the orientation
    of the image will be different. I believe the image will then "lie on
    the side", but you should really try this out if you want to verify it.

    --
    ----------------------------------------------------------------
    Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
    e-mail: pausch at stjarnhimlen dot se
    WWW: http://stjarnhimlen.se/

 

 
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