polarizer or neutral

Discussion in 'Digital Photography' started by Dooban, Feb 11, 2006.

  1. Dooban

    Dooban Guest

    I just bought a Kenko PL 55mm polarizer but seems to be a neutral
    filter instead. When I turn the ring I see no difference in light. Does
    anyone know if that could be a neutral filter o it's just I don't know
    how to turn the ring. I really cannot see a slight difference in light
    through it when turning the ring.

    Thanks for the responses.
    Dooban, Feb 11, 2006
    #1
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  2. Dooban

    Scott W Guest

    Dooban wrote:
    > I just bought a Kenko PL 55mm polarizer but seems to be a neutral
    > filter instead. When I turn the ring I see no difference in light. Does
    > anyone know if that could be a neutral filter o it's just I don't know
    > how to turn the ring. I really cannot see a slight difference in light
    > through it when turning the ring.
    >
    > Thanks for the responses.


    Try pointing the camera up at a blue sky or point at an angle through a
    window and try.

    Scott
    Scott W, Feb 11, 2006
    #2
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  3. Dooban

    Pat Guest

    A google search shows the PL as a polarizing filter, but it's an easy
    check to see if it is.

    Get another polarizing filter if you have one or a pair of polarized
    sun glasses and stack them. Then rotate them against themselves. If
    it is polarized, you can tell. Where the polarizing crosses, it will
    be very dark.

    If there is no change when you rotate it, it is likely circular
    polarization, which is what you generally want on an autofocus lens.

    The other way to test it is to find some glare, preferably outside, and
    look through the lens at it. Inside and other places without much
    glare, a polarizing filter will have little effect.
    Pat, Feb 11, 2006
    #3
  4. Dooban

    Guest

    Like they said, a polariser *is* an ND filter if there is no polarised
    light coming through it...

    Try it on a blue sky near midday. When pointed directly towards or
    away from the sun you will see little or no effect, but when pointed at
    90 degrees to it (eg, skies near the horizon at midday) the effect will
    be dramatic. Try it over river- and ocean- views where there is a lot
    of reflection off the water. Lastly, try it looking at glass windows
    with lots of reflections, but at about 45 degrees, *not* straight on..

    If, after all that, you *still* can't see the difference as you turn
    it, it *is* just an ND filter, or your eyesight is severely challenged!
    , Feb 11, 2006
    #4
  5. Dooban

    Scott W Guest

    Pat wrote:
    > A google search shows the PL as a polarizing filter, but it's an easy
    > check to see if it is.
    >
    > Get another polarizing filter if you have one or a pair of polarized
    > sun glasses and stack them. Then rotate them against themselves. If
    > it is polarized, you can tell. Where the polarizing crosses, it will
    > be very dark.
    >
    > If there is no change when you rotate it, it is likely circular
    > polarization, which is what you generally want on an autofocus lens.
    >


    This depends on both which way you have the filter pointed. If you
    have the front of the filter towards the polarizing sunglasses then you
    see a variation in the transmission as you rotate the filter.

    Scott
    Scott W, Feb 11, 2006
    #5
  6. Dooban

    Jim Townsend Guest

    Dooban wrote:

    > I just bought a Kenko PL 55mm polarizer but seems to be a neutral
    > filter instead. When I turn the ring I see no difference in light. Does
    > anyone know if that could be a neutral filter o it's just I don't know
    > how to turn the ring. I really cannot see a slight difference in light
    > through it when turning the ring.


    If there are two layers with a ring to turn then it's a polarizing filter.
    There's not much point in rotating an ND filter :)
    Jim Townsend, Feb 11, 2006
    #6
  7. Dooban

    Guest

    >If there are two layers with a ring to turn then it's a polarizing filter.
    >There's not much point in rotating an ND filter :)


    'two layers'??

    Linear polarisers don't have two layers. And while I've never used a
    circular, I understood that the 'quarter-wave' thingy was *bonded* to
    the back of the polariser, so it does not have two separate layers as
    you seem to be describing.

    Unless you mean the rotating part of the filter is separate from the
    threaded part, which is sorta self-evident.. I think the OP is
    suggesting that it could be an ND filter accidentally loaded into a
    polariser assembly.
    , Feb 11, 2006
    #7
  8. wrote:

    : Unless you mean the rotating part of the filter is separate from the
    : threaded part, which is sorta self-evident.. I think the OP is
    : suggesting that it could be an ND filter accidentally loaded into a
    : polariser assembly.

    That was the way I read it. If the OP is trying to tell the if this
    properly manufactured filter is a ND filter or a Pola. In this case the
    visual inspection showing that the filter has the ability to turn the
    filter media seperate from the filter threads would identify a Pola. But
    if the incorrect filter media is installed in a filter mount (very
    unlikely but possible) then these tests that use two pola filters,
    counter-rotated against eachother would definatively show that the filter
    media in question is or is not a Pola.

    But as has been pointed out the OP seemed to indicate in the original
    posting that they were unsure if this "Pola" is really a Pola due to not
    seeing powerful changes as the filter is being rotated. And as has been
    pointed out such a drastic optical change may not be evident in all
    situations. And thus it may be simply a case of mistaken expectations on
    the part of the OP. In which case some of the earlier replys probably took
    care of helping the OP and some of the followup "tests" may be able to
    help the OP test the filter in question to ease their own mind.

    IMHO I would suspect that most well known filter manufacturers perform
    some form of quality control and thus the likelyhood of an incorrect
    filter media installed in a Pola filter mount getting out into the public
    is vastly unlikley (not totally impossible but very unlikely). :)

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
    Randy Berbaum, Feb 11, 2006
    #8
  9. Dooban

    Dooban Guest

    Thank you all for the responses. It's incredible the amount of
    knowledge and solidarity one finds in usenet. Finally I am going to
    take a look to my physics 101 book because it seemed I didn't get the
    theory very well. As some of you have pointed out I wasn't looking at
    proper light sources nor accurate angles so I could not see any
    difference when turning the ring. When doing so I realized I have a
    goog PL filter (linear). Thanks :) (blush)
    Dooban, Feb 11, 2006
    #9
  10. Dooban

    imbsysop Guest

    "Dooban" <> wrote in message
    news:...
    >I just bought a Kenko PL 55mm polarizer but seems to be a neutral
    > filter instead. When I turn the ring I see no difference in light. Does
    > anyone know if that could be a neutral filter o it's just I don't know
    > how to turn the ring. I really cannot see a slight difference in light
    > through it when turning the ring.


    a polarizer filter used at the "wrong" angle versus the polarized light will
    just act as an ND filter ..

    FWIW
    imbsysop, Feb 11, 2006
    #10
  11. Dooban

    Guest

    >Thank you all for the responses.

    And thank you, Dooban, for returning to the thread and acknowledging
    the replies! I trust you are aware that a linear polariser may cause
    problems in cameras that use 'beam-splitters' and/or folded light
    paths? In essence that means you need to be careful if using the
    filter on most SLRs, or any other camera with that type of system.
    Linears *can* cause problems with both the focus and exposure, but it
    is still possible to use them successfully.
    , Feb 11, 2006
    #11
  12. Pat <> wrote:
    >
    > The other way to test it is to find some glare, preferably outside, and
    > look through the lens at it. Inside and other places without much
    > glare, a polarizing filter will have little effect.
    >


    A relatively easy test to conduct is to look through the viewfinder at
    reflection on water. The polarizer will easily remove that reflection
    and actually allow you to see into the water if the water is clear
    enough.

    --
    Thomas T. Veldhouse
    Key Fingerprint: 2DB9 813F F510 82C2 E1AE 34D0 D69D 1EDC D5EC AED1
    Thomas T. Veldhouse, Feb 13, 2006
    #12
  13. Dooban

    Dooban Guest

    Thanks Mark for your interest. Yes I am aware of linear polarizers
    problems with SLRs. Mine is a Lumix FZ30 and still don't know if the
    linear would cause any problem, I guess I'll have to check and see, but
    at the moment it woks perfectly well.

    THomas, the main problem I had was not using the correct angle against
    the Sun when focusing to a reflection. When at 45º the filter works as
    it should. Thanks anyway.
    Dooban, Feb 13, 2006
    #13
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