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  1. #1
    jtaylor's Avatar
    jtaylor Guest

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough



    Haven't started a focuser yet. What advantages are there to 2" eyepieces,
    and are they important with this size telescope?



  2. #2
    Mean Mr Mustard's Avatar
    Mean Mr Mustard Guest

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough

    FOV


  3. #3
    Orion's Avatar
    Orion Guest

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough

    The 1st time you look thru a 2" at the Orion nebula, or the Pleiades, et al,
    you'll wonder why you didn't upgrade in the first place. It is well worth
    doing...
    Clearskies!
    Orion

    "jtaylor" <jtaylor@deletethis.hfx.andara.com> wrote in message
    news:2Euhe.5851$5u4.20560@nnrp1.uunet.ca...



  4. #4
    Brian Tung's Avatar
    Brian Tung Guest

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough

    jtaylor wrote:

    They're more useful as missile weapons, and you'll need them if you're
    not adept and hand-to-hand combat.

    Mostly, it's field of view, which has two distinct benefits. One is
    that you're better able to frame large objects, like the Pleiades or
    the Orion Nebula. The other big benefit is that with a large FOV, it's
    easier to locate objects and to match what you're seeing with what's on
    your star atlas or planetarium program.

    As far as the size of your telescope is concerned, I think an 8-inch
    reflector probably should get a 2-inch focuser (you can always put in
    an adapter to use 1-1/4-inch eyepieces), but the real parameter of
    interest is the focal length. That is what determines the maximum
    field of view available with 1-1/4-inch vs 2-inch eyepieces.

    For instance, a typical 8-inch reflector is f/6, meaning the focal
    length is about 48 inches, or 1200 mm. At that length, you can get
    up to about 2.3 degrees of true field with a 2-inch eyepiece, and
    about 1.5 degrees with a 1-1/4-inch eyepiece. At any focal length,
    of course, the gain in the true field of 2-inch eyepieces over the
    1-1/4 inchers is 60 percent by width, and about 150 percent by area.
    It's pretty substantial.

    Brian Tung <brian@isi.edu>
    The Astronomy Corner at http://astro.isi.edu/
    Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
    The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
    My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

  5. #5
    Stephen Paul's Avatar
    Stephen Paul Guest

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough


    "Brian Tung" <brian@isi.edu> wrote in message
    news:d65vbo$s7a$1@zot.isi.edu...

    In kind, at F4, the excepted norm of 6mm maximum exit pupil is provided by a
    24mm eyepiece. My 800mm focal length F4 Newt doesn't really gain much with a
    2" eyepiece. The 24mm Pan gives a Tfov of 2 degrees at 33x at max exit
    pupil.



  6. #6
    Brian Tung's Avatar
    Brian Tung Guest

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough

    Stephen Paul wrote:

    That's a good point. It's worth pointing out, though, that I don't
    notice the shadow of the secondary under dark skies when I'm using my
    55 mm Plossl on my 10-inch f/6 reflector, which yields a 9 mm exit
    pupil (considerably larger than my own pupil). I don't know the
    secondary minor axis off hand, but I'm sure it's about 2 inches across,
    meaning that at the eye relief distance, its shadow is a bit less than
    2 mm across. That means that you can avoid noticeable vignetting under
    dark skies, although you do have to be a little careful where you put
    your eyeball, exactly.

    Brian Tung <brian@isi.edu>
    The Astronomy Corner at http://astro.isi.edu/
    Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
    The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
    My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

  7. #7
    Llanzlan Klazmon's Avatar
    Llanzlan Klazmon Guest

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough

    "jtaylor" <jtaylor@deletethis.hfx.andara.com> wrote in
    news:2Euhe.5851$5u4.20560@nnrp1.uunet.ca:


    Wider field of view for a given magnification. I would say go for a 2"
    focuser with a 1 1/4 adapter. Remember though that a good quality 2"
    eyepiece could cost more than your entire scope. The prime example being
    the 31mm Nagler.

    Klazmon.


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

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough

    > Wider field of view for a given magnification. I would say go for a 2"

    I agree that a 2" focuser is pretty much a no-brainer - get one. However,
    it is not the case that a "good quality" 2" eyepiece needs to cost a lot.
    I have tried a number of them, each costing less than $100, that I consider
    very useable. Of course, your criteria for what is "good quality" may
    differ from mine, so you should try and test them before buying.

    Also, get a 2" UHC or OIII to go with your 2" wide-field eyepiece.

    Dennis



  9. #9
    Llanzlan Klazmon's Avatar
    Llanzlan Klazmon Guest

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough

    "Dennis Woos" <dpwoos@gmavt.net> wrote in
    news:118frad2ih4qv25@corp.supernews.com:


    That is why I said "could cost".

    Klazmon.







  10. #10
    james's Avatar
    james Guest

    Default Building 8" reflector - 2" eyepiece or is 1.25" enough

    On Sat, 14 May 2005 22:31:13 GMT, "Orion" <mark.bender@syntegra.com>
    wrote:

    ******

    I have seen some very nice complete views of M42 with a 60MM and 0.965
    eyepiece.

    james


 

 
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