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  1. #1
    Ioannis's Avatar
    Ioannis Guest

    Default 45 degree diagonal



    So much for the new 45 degree diagonal I ordered from Apogee. It's a
    complete disaster. I don't recall who said it was meant for terrestial
    viewing, but I'll tell you that for star splitting, it's useless.

    Unless the star image is in perfect focus, there are two images
    uncombined which resemble a split binary with members of equal magnitude.

    Last year, I was able to cleanly split Ras Algheti at 5" with my Tasco
    and its own junk EPs in 2 minutes, this year it took me 20 minutes to
    finally see the companion and after endless tries focusing and
    refocusing the Apogee zoom EP. The zoom EP is good though.

    What a complete waste! Warning! NEVER buy a 45 deg diagonal for astro
    viewing! Guess I had to learn the hard way...
    --
    I. N. Galidakis
    http://users.forthnet.gr/ath/jgal/
    ------------------------------------------
    Eventually, _everything_ is understandable


  2. #2
    Brian Wirthlin's Avatar
    Brian Wirthlin Guest

    Default 45 degree diagonal

    Typically a 45 degree diagonal has a roof prism to reverse the image
    left to right. This requires the roof angle be 90 +/- seconds of arc
    to avoid a double image in the horizontal axis. I'm told the roof
    needs a coating of some specific properties to avoid a degradation of
    resolution in that axis too. I don't understand this, but as Warren
    Smith was the one who said it I'm willing to assume it's true. It's
    not impossible to make a good prism of this type, but it's not easy.
    When you get down to it there are going to be production variations in
    this kind of prism, and I've seen very experienced people approve roof
    prisms with this kind of error. (It's really obvious on an
    interferometer, or even with a star test, but a resolution test needs
    to be done with care.) Don't assume that your one example is
    representative of the design.

    Brian


    Ioannis <morpheus@olympus.mons> wrote in message news:<1092094759.618762@athnrd02>...

 

 

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