Now that Nikon is outselling Canon....

Discussion in 'Nikon' started by RichA, Oct 8, 2007.

  1. RichA

    Tony Polson Guest

    I'm not exactly sure how it works, but certain lenses do exhibit a
    change in the plane of sharp focus as the lens aperture is changed.

    One example is the Carl Zeiss C Sonnar ZM 50mm f/1.5 which is made
    with the Leica M mount. Apparently, at typical portrait focusing
    distances, the plane of sharp focus changes significantly between wide
    open and stopped down to, say, f/8. By "significantly" I mean by
    several centimetres, even by several inches.

    This lens is an updated near- copy of the legendary Carl Zeiss Sonnar
    for the Contax series of rangefinder cameras. It has certain
    distinctive qualities which endear it to its aficionados, notably its
    wide open very sharp central rendition gradually getting softer away
    from the optical axis with a distinctly soft rendition at the edges.

    When used stopped down, the plane of sharp focus changes
    significantly, leading users who would expect a greater depth of field
    around the point of sharp focus to be somewhat disappointed, because
    the plane of sharp focus has moved away from that indicated by the
    opto-mechanical rangefinder.

    I haven't yet had the opportunity to test the C Sonnar ZM 50mm f/1.5,
    but it sounds as though the 58mm f/1.2 NOCT-Nikkor may have a similar
    problem. Having the benefit of through the lens viewing might be
    thought to be better than an opto-mechanical rangefinder with a lens
    with this characteristic, but in practice it is no help because we all
    focus with the lens wide open!

    It is perhaps worth noting that the Leica 50mm f/1 Noctilux has no
    such problem, being essentially a lens that is without any particular
    vices except for its well-known harsh bokeh wide open, something that
    we should learn to forgive in an otherwise superlative optic. In
    contrast, the NOCT-Nikkor is optimised for use wide open, with
    performance falling away as you stop down, whereas the Leica Noctilux
    works extremely well across its whole range of apertures.
    Tony Polson, Oct 14, 2007
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  2. A lens with a significant amount of overall spherical aberration
    can show some focus shift. Ansel Adams documented this. However,
    the Noct was specifically designed to minimize spherical aberrations.
    Nor would the effective loss of aperture from the focusing system
    trigger such a focus shift since the iris isn't blocking any
    incoming light.
    Michael Benveniste, Oct 14, 2007
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  3. Certainly on my Nikon cameras, stopping down a 50/1.4 to f/2.0 has no
    visible effect in the viewfinder. I don't know if it is the Fresnel lens
    that's causing it or something else.
    Philip Homburg, Oct 14, 2007
  4. RichA

    Tony Polson Guest

    I wasn't commenting on the NOCT, I merely pointed out a possible
    analogy with the Zeiss C Sonnar.
    Tony Polson, Oct 15, 2007
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