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  1. #1
    Don Fritz's Avatar
    Don Fritz Guest

    Default 13mm Nagler Type 6 F.O.V. ?



    I have used the new 13mm Nagler for about 2 months in my 13.1" F/4.5 dob. I
    find that with my eye centered and almost pressed against the eyelens I
    cannot see the edge of the field. To see the edge in any direction I must
    move my eye position slightly off center to the opposite side. The usuable
    field appears about like a Radian and not as sharp on axis. Has anyone else
    noticed this? Don



  2. #2
    John Bevan's Avatar
    John Bevan Guest

    Default 13mm Nagler Type 6 F.O.V. ?

    In article
    <xxlxb.118711$Ec1.5101558@bgtnsc05-news.ops.worldnet.att.net>,
    "Don Fritz" <dfritz@worldnet.att.net> wrote:

    I have the same experience with Naglers, at least the ones I've used. I
    am unable see the full AFOV with my eye in the optimum position (iris
    coincident with the exit pupil). I own one Nagler - a 7mm Type 1 which
    happens to be my favorite eyepiece for DSOs through my 8" f/6. Still, I
    suspect that a 7mm Pentax XL with a 65 deg AFOV would show essentially
    the same view and be just as satisfactory. If there was a 7mm Radian,
    it might do the job, too. As for sharpness on axis, I really don't have
    a firm preference between the quality eyepieces. For me, the telescope
    objective (a Zambuto mirror in my case) is the main determinant of image
    quality.

    The extreme AFOV of Naglers (and Meade UWAs) obviously satisfies a lot
    of amateurs so you can't argue with success. However, when you
    calculate the true field from the field stop of these eyepieces and
    relate it to the focal length and magnification I think you find that
    the 82 degree apparent field is somewhat of an illusion and is enhanced
    by the pincushion distortion inherent in the design. If there were no
    pincushion distortion, I believe the AFOVs would be in the 70s.

    John

  3. #3
    Kilolani's Avatar
    Kilolani Guest

    Default 13mm Nagler Type 6 F.O.V. ?

    I agree... but then Televue is not marketing the "usable" portion of the
    field, they are marketing the "spacewalk" effect... which is fairly unique
    to Naglers.

    "John Bevan" <johnxbevan@nospamlink.net> wrote in message
    news:johnxbevan-A901BA.20504527112003@news01.east.earthlink.net...
    dob. I
    must
    usuable
    else



 

 

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