Do I need a thin polarizer for a Minolta 17-35mm lens?

Discussion in 'Minolta' started by David Farber, Nov 15, 2005.

  1. David Farber

    no_name Guest

    I think he's concerned that at 17mm the FRAME of the filter might
    vignette the image. I've seen this with wide angle lenses in film. The
    corners are just chopped off, like shooting through a knot-hole.

    I don't know if the "thin" polarizers will actually work for this or
    not, but that's what they're advertised for.

    I used step-up rings and a larger diameter filter to overcome this, i.e.
    step-up ring mounted on a lens with 52mm front thread, and 58mm
    polarizer mounted on the step-up ring.

    With a 77mm front thread, you'd have to go to something like 82mm or
    86mm to do this, and at that size the good quality filters ain't cheap.

    OTOH step-up rings themselves are relatively cheap, so you can buy them
    for all your lenses & use the same polarizer that's sized for the
    wide-angle lens with your other lenses.
    no_name, Nov 16, 2005
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  2. Polarization occurs naturally when light reflects from a smooth
    surface. The light waves line up so that the waves vibrate in a certain
    plane, much like a rope that is shaken up and down or left and right.
    The light reflecting from a shiny road ('glare') can be removed with
    'polarized' sunglasses.

    What fits on your camera is not a polarizer at all, but an analyzer. It
    does not CREATE polarized light, but merely allows polarized light to
    pass or no to pass, depending on the angle that the analyzer is rotated
    with respect to the polarized light.

    If the analyzer is at right angles to the plane of polarization of
    polarized light, little or no polarized light will pass through.

    uraniumcommittee, Nov 16, 2005
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  3. David Farber

    David Farber Guest

    So you're saying that the statement, "The second issue with polarizers and
    very wide-angle lenses is the thickness of the filter. By their nature
    polarizers are thick filters because they have a double ring — the first of
    which mounts the filter to the lens and the second which is the rotating
    polarizing element itself. If the lens is wider than about 24mm, when used
    at SMALL apertures the edge of the ring can cause vignetting at the corners
    of the frame," is incorrect? (capitalization of "small" for emphasis added
    by me)

    Thanks for your reply.
    David Farber, Nov 16, 2005
  4. David Farber

    Matt Clara Guest

    Since an aperture is actually defined as an opening, I'd say "small
    openings" is exactly right. The aperture number we get (called an f stop)
    on our cameras is actually a ratio between focal length and aperture
    diamter; thus f16 is a diaphragm aperture opening 1/16 the size of the focal
    length. That's why it's always the same, no matter what lens you use.
    Matt Clara, Nov 16, 2005
  5. David Farber

    David Farber Guest

    I was just taking issue with the way the information was presented at that
    luminous-landscape tutorial website. It seems directly opposite to the
    information I am receiving here. I was focusing (no pun intended) on the
    small aperture causing vignetting issue. I seemed to have confused everyone
    early on when I asked if they meant small f/stop number or small aperture. I
    understand the difference very well. I was just trying to come up with a
    theory that would explain why that website said that small apertures would
    cause vignetting problems while the opposite was being said on this ng.

    Thanks for your reply.
    David Farber, Nov 16, 2005
  6. David Farber

    Paul Mitchum Guest

    They didn't say that small apertures would cause vignetting problems...
    They said that the obtrusive size of the filter ring could cause
    vignetting problems, especially at 'small' apertures.

    I think they just wrote it wrong. Closing the aperture helps reduce some
    vignetting/fall-off problems, but if the problem comes from the size of
    a filter, get a thinner filter to make the problem go away while using
    your fancy f/2.8 zoom wide open. :)
    Paul Mitchum, Nov 17, 2005
  7. David Farber

    Sander Vesik Guest

    what if there is no sky in the shot? polarizer is hardly limited
    to the sky or for that matter, atmospheric effects.
    Sander Vesik, Nov 17, 2005
  8. It would depend on the angle of the surface involved and other factors.
    uraniumcommittee, Nov 17, 2005
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