Reflections from plexiglass?

Discussion in 'Digital Photography' started by JoeB, Jul 27, 2005.

  1. JoeB

    JoeB Guest

    Recently I was trying to shoot through plexiglass, using a Hoya circular
    polariser to try and cut reflections - without much success. The
    reflections were reduced a bit, but not eliminated.

    Has anyone else experienced this? I was wondering if reflections on
    plexiglass were somehow harder to kill than on "normal" glass, or whether a
    higher-quality polariser would have done a better job...

    Anyone have any insights?

    Thanks -

    Joe

    --
    The address in the headers is a spamtrap - please use joe at fallingonion
    dot com if you prefer to use email.
     
    JoeB, Jul 27, 2005
    #1
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  2. JoeB

    Old Bugger Guest

    On Wed, 27 Jul 2005 09:40:49 +0100, JoeB <> wrote:

    >Recently I was trying to shoot through plexiglass, using a Hoya circular
    >polariser to try and cut reflections - without much success. The
    >reflections were reduced a bit, but not eliminated.
    >
    >Has anyone else experienced this? I was wondering if reflections on
    >plexiglass were somehow harder to kill than on "normal" glass, or whether a
    >higher-quality polariser would have done a better job...
    >
    >Anyone have any insights?


    If you can, hold the lens tight against the reflecting surface.
     
    Old Bugger, Jul 27, 2005
    #2
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  3. JoeB

    Guest

    >Has anyone else experienced this? I was wondering if
    >reflections on plexiglass were somehow harder to kill
    >than on "normal" glass, or whether a higher-quality polariser
    >would have done a better job...


    Not really, but plexiglass is often covered with very fine scratches
    from wear or polishing, and may be less clear than glass, which makes
    the problems worse.

    No polariser will kill reflections perfectly, and the efficacy of
    polarising will depend on the amount of polarised light contained in
    the reflection, which in turn depends on the angle of the reflection -
    around 45 degrees to the glass will tend to give the best results. I
    suspect *that* might have been your problem. If you were pretty well
    straight on, the polariser will do very little for you.


    High qulaity polarisers usually have good multicoating and very flat
    optical surfaces, rather than much more polarising ability.

    Like OB said, best to get close, and avoid them altogether..
     
    , Jul 27, 2005
    #3
  4. JoeB

    SimonLW Guest

    "JoeB" <> wrote in message
    news:1sptm49bqozyh$...
    > Recently I was trying to shoot through plexiglass, using a Hoya circular
    > polariser to try and cut reflections - without much success. The
    > reflections were reduced a bit, but not eliminated.
    >
    > Has anyone else experienced this? I was wondering if reflections on
    > plexiglass were somehow harder to kill than on "normal" glass, or whether

    a
    > higher-quality polariser would have done a better job...
    >
    > Anyone have any insights?
    >
    > Thanks -
    >
    > Joe
    >
    > --
    > The address in the headers is a spamtrap - please use joe at fallingonion
    > dot com if you prefer to use email.


    It depends on the angle of the incident light. The polarizer is most
    effective at what's known as Brewster's angle and is related to the
    material's refractive index.

    Some plastics will not work well with polarizer filters because stresses may
    show as colored reflections and patterns through the polarizer. This is not
    a common problem with acrylic (aka Plexiglas, Lucite...). Some other types
    of clear plastics are mistaken for acrylic.
    -S
     
    SimonLW, Jul 27, 2005
    #4
  5. JoeB

    Don Stauffer Guest

    JoeB wrote:
    > Recently I was trying to shoot through plexiglass, using a Hoya circular
    > polariser to try and cut reflections - without much success. The
    > reflections were reduced a bit, but not eliminated.
    >
    > Has anyone else experienced this? I was wondering if reflections on
    > plexiglass were somehow harder to kill than on "normal" glass, or whether a
    > higher-quality polariser would have done a better job...
    >
    > Anyone have any insights?
    >
    > Thanks -
    >
    > Joe
    >



    Going a little off-topic, how does a circular polarizer work, anyway. I
    understand how a linear polarizer works- you just rotate the polarizer
    to right angles to plane of polarization of glare, and it virtually
    eliminates it.

    With a circular polarizer what actually happens- how do you use it to
    discriminate against a polarizing glare, or polarized skylight? Does it
    automatically remove any linear polarized light?
     
    Don Stauffer, Jul 27, 2005
    #5
  6. JoeB wrote:
    > Recently I was trying to shoot through plexiglass, using a Hoya
    > circular polariser to try and cut reflections - without much success.
    > The reflections were reduced a bit, but not eliminated.
    >
    > Has anyone else experienced this? I was wondering if reflections on
    > plexiglass were somehow harder to kill than on "normal" glass, or
    > whether a higher-quality polariser would have done a better job...
    >
    > Anyone have any insights?
    >
    > Thanks -
    >
    > Joe


    You may need to polarize the light as well as at the lens.

    --
    Joseph Meehan

    Dia duit
     
    Joseph Meehan, Jul 27, 2005
    #6
  7. JoeB

    Owamanga Guest

    On Wed, 27 Jul 2005 16:15:02 GMT, "Joseph Meehan"
    <> wrote:

    >JoeB wrote:
    >> Recently I was trying to shoot through plexiglass, using a Hoya
    >> circular polariser to try and cut reflections - without much success.
    >> The reflections were reduced a bit, but not eliminated.
    >>
    >> Has anyone else experienced this? I was wondering if reflections on
    >> plexiglass were somehow harder to kill than on "normal" glass, or
    >> whether a higher-quality polariser would have done a better job...
    >>
    >> Anyone have any insights?
    >>
    >> Thanks -
    >>
    >> Joe

    >
    > You may need to polarize the light as well as at the lens.


    Grab the sun, turn it 45 degrees, blow fingers.

    --
    Owamanga!
    http://www.pbase.com/owamanga
     
    Owamanga, Jul 27, 2005
    #7
  8. JoeB

    ecm Guest

    Don Stauffer wrote:
    SNIP
    >
    > Going a little off-topic, how does a circular polarizer work, anyway. I
    > understand how a linear polarizer works- you just rotate the polarizer
    > to right angles to plane of polarization of glare, and it virtually
    > eliminates it.
    >
    > With a circular polarizer what actually happens- how do you use it to
    > discriminate against a polarizing glare, or polarized skylight? Does it
    > automatically remove any linear polarized light?


    Here's an answer to that question I found a few months ago:

    "Certain camera optical systems employ internal surfaces that
    themselves polarize light. Using a standard (linear) polarizer will
    cause the light to be further absorbed by the internal optics,
    depending on the relative orientation. A Circular Polarizer is a
    linear one to which has been added,on the side facing the camera, a
    quarter wave "retarder." This "corkscrews" the plane of polarization,
    effectively depolarizing it, eliminating the problem. The Circular
    Polarizer otherwise functions in the same manner."

    Ira Tiffen, Tiffen Company, at:
    http://www.tiffen.com/camera_filters.htm

    What that actually MEANS, I'm not at all certain.....
    ECM
     
    ecm, Jul 27, 2005
    #8
  9. JoeB

    Owamanga Guest

    On Wed, 27 Jul 2005 09:31:12 -0500, Don Stauffer
    <> wrote:

    >Going a little off-topic, how does a circular polarizer work, anyway. I
    >understand how a linear polarizer works- you just rotate the polarizer
    >to right angles to plane of polarization of glare, and it virtually
    >eliminates it.


    As far as using it in the field, they both work the same way. And they
    both result in the same image. The difference is how polarized the
    light is once it exits the filter. The negative/sensor cares not, but
    the AF and metering systems do care. So on a CPL extra quarter-wave
    retarder magic is applied that depolarizes the light again before it
    exits the filter.

    CPLs have a front and a back, regular PLs will work either way round.

    A PL can be used to polarize a light source (strap one over your flash
    gun for example), but a CPL can only do this in one direction.

    >With a circular polarizer what actually happens- how do you use it to
    >discriminate against a polarizing glare, or polarized skylight? Does it
    >automatically remove any linear polarized light?


    Use it just the same as your regular polarizer.

    --
    Owamanga!
    http://www.pbase.com/owamanga
     
    Owamanga, Jul 27, 2005
    #9
  10. JoeB

    JoeB Guest

    On Wed, 27 Jul 2005 09:57:08 GMT, Old Bugger wrote:

    > On Wed, 27 Jul 2005 09:40:49 +0100, JoeB <> wrote:
    >
    >>Recently I was trying to shoot through plexiglass, using a Hoya circular
    >>polariser to try and cut reflections - without much success. The
    >>reflections were reduced a bit, but not eliminated.
    >>
    >>Has anyone else experienced this? I was wondering if reflections on
    >>plexiglass were somehow harder to kill than on "normal" glass, or whether a
    >>higher-quality polariser would have done a better job...
    >>
    >>Anyone have any insights?

    >
    > If you can, hold the lens tight against the reflecting surface.


    In the end, doing just that without the filter gave the best results... I
    was just wondering if the plexiglass (or acrylic, or whatever it was) had
    anything to do with it.
    As has become clear from the other replies downthread it's far more likely
    that I didn't pay enough attention to where the light source was - I need
    to learn more about how polarisers work :)

    Joe
    --
    The address in the headers is a spamtrap - please use joe at fallingonion
    dot com if you prefer to use email.
     
    JoeB, Jul 28, 2005
    #10
  11. JoeB

    JoeB Guest

    On 27 Jul 2005 03:11:08 -0700, wrote:

    >>Has anyone else experienced this? I was wondering if
    >>reflections on plexiglass were somehow harder to kill
    >>than on "normal" glass, or whether a higher-quality polariser
    >>would have done a better job...

    >
    > Not really, but plexiglass is often covered with very fine scratches
    > from wear or polishing, and may be less clear than glass, which makes
    > the problems worse.
    >
    > No polariser will kill reflections perfectly, and the efficacy of
    > polarising will depend on the amount of polarised light contained in
    > the reflection, which in turn depends on the angle of the reflection -
    > around 45 degrees to the glass will tend to give the best results. I
    > suspect *that* might have been your problem. If you were pretty well
    > straight on, the polariser will do very little for you.


    I suspect you're right - the light would have been coming in over my
    shoulder, nowhere near 45 degrees. As such the polariser had an effect,
    just not as pronounced an effect as I was expecting. I need to read up on
    polarisers...

    > High qulaity polarisers usually have good multicoating and very flat
    > optical surfaces, rather than much more polarising ability.
    >
    > Like OB said, best to get close, and avoid them altogether..


    Turns out that was the way :)

    Joe
    --
    The address in the headers is a spamtrap - please use joe at fallingonion
    dot com if you prefer to use email.
     
    JoeB, Jul 28, 2005
    #11
  12. JoeB

    Don Stauffer Guest

    ecm wrote:
    >
    > Don Stauffer wrote:
    > SNIP
    >
    >>Going a little off-topic, how does a circular polarizer work, anyway. I
    >>understand how a linear polarizer works- you just rotate the polarizer
    >>to right angles to plane of polarization of glare, and it virtually
    >>eliminates it.
    >>
    >>With a circular polarizer what actually happens- how do you use it to
    >>discriminate against a polarizing glare, or polarized skylight? Does it
    >>automatically remove any linear polarized light?

    >
    >
    > Here's an answer to that question I found a few months ago:
    >
    > "Certain camera optical systems employ internal surfaces that
    > themselves polarize light. Using a standard (linear) polarizer will
    > cause the light to be further absorbed by the internal optics,
    > depending on the relative orientation. A Circular Polarizer is a
    > linear one to which has been added,on the side facing the camera, a
    > quarter wave "retarder." This "corkscrews" the plane of polarization,
    > effectively depolarizing it, eliminating the problem. The Circular
    > Polarizer otherwise functions in the same manner."
    >
    > Ira Tiffen, Tiffen Company, at:
    > http://www.tiffen.com/camera_filters.htm
    >
    > What that actually MEANS, I'm not at all certain.....
    > ECM
    >

    It explains why the new cameras need the circular polarizer, but the
    statement "otherwise functions in the same manner" seems strange to me-
    I don't understand it. .
     
    Don Stauffer, Jul 28, 2005
    #12
  13. Old Bugger <> writes:

    > On Wed, 27 Jul 2005 09:40:49 +0100, JoeB <> wrote:
    >
    > >Recently I was trying to shoot through plexiglass, using a Hoya circular
    > >polariser to try and cut reflections - without much success. The
    > >reflections were reduced a bit, but not eliminated.
    > >
    > >Has anyone else experienced this? I was wondering if reflections on
    > >plexiglass were somehow harder to kill than on "normal" glass, or whether a
    > >higher-quality polariser would have done a better job...
    > >
    > >Anyone have any insights?

    >
    > If you can, hold the lens tight against the reflecting surface.


    With a rubber lens-hood; in addition to making a better light seal,
    this also lets you adjust your angle a small amount.
    --
    David Dyer-Bennet
    Recovering from server meltdown! Email and web service on www.dd-b.net
    including all virtual domains (demesne.com, ellegon.com, dragaera.info,
    mnstf.org, and many others) is rudimentary and intermittent.
     
    David Dyer-Bennet, Jul 28, 2005
    #13
  14. JoeB

    ecm Guest

    Don Stauffer wrote:
    > ecm wrote:
    > >
    > > Don Stauffer wrote:

    SNIP
    > > effectively depolarizing it, eliminating the problem. The Circular
    > > Polarizer otherwise functions in the same manner."
    > >
    > > Ira Tiffen, Tiffen Company, at:
    > > http://www.tiffen.com/camera_filters.htm
    > >


    > It explains why the new cameras need the circular polarizer, but the
    > statement "otherwise functions in the same manner" seems strange to me-
    > I don't understand it.


    In the context of the article I think he's saying that, "The Circular
    Polarizer otherwise functions in the same manner [as a linear
    polarizer]." That's been my experience with a (Hoya) circular
    polarizer; it doesn't function any differently than a regular one - it
    even blacks out when I'm wearing polarized sunglasses and it's at the
    right angle.

    According to some (including Mr. Tiffen in the article above) the
    circular polarizers are only necessary in autofocus SLR's, not other
    cameras or digicams; it's an issue with the partially transmissive
    mirror being polarized (so you would cancel all light transmission if
    they're at 90 degrees to each other). OTOH, some sites talk about
    problems with autofocus in digicams. I haven't tried a linear polarizer
    on my digicam, so I don't know.... circular works fine, though.

    ECM
     
    ecm, Jul 28, 2005
    #14
  15. JoeB

    ASAAR Guest

    On Thu, 28 Jul 2005 09:15:11 -0500, Don Stauffer wrote:

    >> A Circular Polarizer is a
    >> linear one to which has been added,on the side facing the camera, a
    >> quarter wave "retarder." This "corkscrews" the plane of polarization,
    >> effectively depolarizing it, eliminating the problem. The Circular
    >> Polarizer otherwise functions in the same manner."

    >
    > It explains why the new cameras need the circular polarizer, but the
    > statement "otherwise functions in the same manner" seems strange to
    > me- I don't understand it. .


    I think it means that even though it has an additional quarter
    wave "retarder" which "corkscrews" the plane of polarization, the
    shouldn't worry that circular polarizers will produce a different
    effect than linear polarizers. Of course CP's reason for existence
    is the different effect produced inside some cameras, so I suppose
    external differences could be devised. But for the usual intended
    purposes (sky, reflections, etc.) they should produce the same
    results.
     
    ASAAR, Jul 28, 2005
    #15
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