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• #22775 .mf veterán .mf #22766

  Új Válasz 2013-01-14 17:46:04 #22775

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  veterán

  válasz .mf #22766 üzenetére

  Egy kis kereséssel úgy tűnik találtam egy választ, ami (amíg a Kodak szabadalom él), nem sok jóval kecsegtet:

  [link]

  Telescope focal reducers are symmetrical paired achromats, and encounter the reduction in back focus that John Tran mentioned. The solution to that is to simply make them asymmetrical. At that point, they're generally referred to as "wideconverters" rather than "focal reducers".
  [...]
  Tommy Lee's "theory" (actually, both optical theory and "manufacturer conspiracy" theory) are incorrect. The big problem is Kodak. They have a very broad patent on the wide converter concept. US Patent 5,499,069, and parallel filings in other countries. Claim 1 is the kicker: it covers any focal reducer that maintains the backfocus of an existing lens.
  [...]
  The thing that gets in the way of all wide converter production, whether my little shop or bigger houses like Kenko, Tamron, Sigma, or Tokina, or even Nikon or Canon trying their hand, is that annoying Kodak patent.
  To this date, only two people have gotten around this:
  •Olympus built the wide converters permanently into the backs of lenses. Their 35-100mm f2.0 and 14-35mm f2.0 are perfectly ordinary 70-200mm f2.8 and 28-70mm f2.8 designs, with integrated 0.5x wide converters.
  •The Nikon/Fuji joint effort called the E2 had a wide converter permanently mounted in the camera.
  The big problem with both of these is fast lenses. The Nikon/Fuji had an optical path wide enough for an f2.8 output, which meant that it limited any lens faster than f5.6 to f5.6 when used with the E2. The Oly converters have f2.0 outputs, so lenses that should have ended up f1.4 zooms after 0.5x conversion instead are choked back to f2.

  My fastest 1.5x also had an f2.0 output, so if you put it on an 85mm f1.4, you got a 56mm f2.0, with nowhere near the quality of an old CZJ or Jupiter in that range.

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