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Wide-angle [was Re: Sub $100 binoculars]

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  • Ed Cannon
    ... It turns out that the 8x42 Ultraviews are wide-angle (8.2-deg true, 65 apparent FOV) and have significant edge softness . This was only the second
    Message 1 of 37 , Jan 31, 2004
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      --- In telescopes@yahoogroups.com, Geoff Gaherty wrote:

      > Wide angle binoculars are not too popular with astronomers
      > because the optical correction towards the edge of the
      > field is usually quite poor.... I expect you would find
      > them quite disappointing after your experience with the
      > excellent Ultraviews.

      It turns out that the 8x42 Ultraviews are wide-angle (8.2-deg
      true, 65 apparent FOV) and have significant "edge softness".
      This was only the second binocular I've bought, and I haven't
      looked through very many others yet. The edge softness is
      not too much of a problem for me, but I can understand why it
      is for others. I hadn't noticed it in my 10x50s, 6.5-deg
      true, 65 apparent FOV, but now that I know to look for it in
      them, it's there, though definitely less noticeable. If I
      understand correctly, it is the width of the actual true
      field of view that causes this (?).

      Ed Cannon - Austin, Texas
    • Phil Harrington
      ... It has to do with several factors, Ed, but primarily the optical design of the eyepieces themselves. If they re using either Kellner or Erfle eyepieces --
      Message 37 of 37 , Feb 1, 2004
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        --- In telescopes@yahoogroups.com, "Ed Cannon" <ecannon@m...> wrote:

        > It turns out that the 8x42 Ultraviews are wide-angle (8.2-deg
        > true, 65 apparent FOV) and have significant "edge softness".
        > This was only the second binocular I've bought, and I haven't
        > looked through very many others yet. The edge softness is
        > not too much of a problem for me, but I can understand why it
        > is for others. I hadn't noticed it in my 10x50s, 6.5-deg
        > true, 65 apparent FOV, but now that I know to look for it in
        > them, it's there, though definitely less noticeable. If I
        > understand correctly, it is the width of the actual true
        > field of view that causes this (?).


        It has to do with several factors, Ed, but primarily the optical
        design of the eyepieces themselves. If they're using either Kellner
        or Erfle eyepieces -- and most do -- then edge distortion is almost
        inevitable regardless of field of view. Some models, like Fujinon's
        FMT-SXs, put in a field flattener element to get rid of distortion.
        Of course, you'll have to pay for this perfection.

        Phil
        ----------------------
        Phil Harrington
        Author, Star Ware
        http://www.philharrington.net
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