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Comments on 66 Petzval ED Semi APO Design

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  • scottatwin
    The 66 Petzval scope is fun to use, but one should know that it is not of the classic Petzval design. In a classic Petzval design the front doublet has twice
    Message 1 of 1 , Dec 31, 2005
      The 66 Petzval scope is fun to use, but one should know that it is
      not of the classic Petzval design. In a "classic" Petzval design the
      front doublet has twice the focal length as the system and the rear
      has a focal length equal to the system. For a 400mm focal length
      scope then the front doublet would have a 800 mm focal length and
      the rear would have an 400mm focal length. The spacing between the
      two lens groups would be 400mm. The WO 66 Petzval design deviates
      greatly from the classis design. The front doublets focal length is
      about 590mm and the rear is about 710mm with a spacing of between
      185mm and 225mm. The spacing depends on the focus tube position.
      Because of the deviation from the classic design one should not
      assume all of the typical properties of a Petzval design. For
      example, though the WO 66 Petzval has a flatter field than would be
      expected from a 400mm doublet,it is not as flat as would be expected
      from the "classic" Petzval design. I believe the field curvature of
      the WO 66 Petzval is similar to a 600 to 800 mm doublet. (About .2mm
      at 10mm off of center)I need to measure this more closely,but I am
      reasonable sure it is in this range. I believe a classic Petzval
      design would produce less than half this curvature. Has anyone else
      measured the field curvature of this scope? I would like to here
      your results.
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