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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.

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.

>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..

"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

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?

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

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

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

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

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.