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  1. B

    Binocular length

    Don't know about DOF but I was able to measure distances of a mile, maybe more, with the 317mm Dall Kirkham, 4650mm focal length, just by the focus position of the eyepiece compared to the stars. So I don't think the DOF was that great, although it could be. I don't think the 317mm aperture was...
  2. B

    Binocular length

    400 years maybe.
  3. B

    Binocular length

    Hi Peter, Post 8. Try collimating a 20.5 inch f/3.9 Newtonian single handedly, even though it has a 1/20th wave mirror. An ancient 6 inch f/8 secondhand AE Newtonian was amazingly good. Unfortunately Jim Hysom, master optician (AE Optics) passed away recently. He made most of the better U.K...
  4. B

    Binocular length

    Longer focal length objectives have less aberrations. In addition, the eyepiece will be a longer focal length, giving more eye relief generally and a simpler design. However, a longer focal length eyepiece may not have such a wide field. The Takahashi 22x60 is, I think, an example, maybe f/6...
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