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Polarizer advice

 
 
Mike
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      10-12-2004
Hi, I am looking into buying a polarizing filter to use on a Canon 10D. I've been reading up about this aspect of photography on various websites and I came across one which mentions the difference between Linear and Circular polarizers. Here's what it says about Circular Polarizers:

CIRCULAR POLARIZER
Provides the same filter effects as a Linear Polarizer, but is designed to work with auto focus cameras with beam splitting metering. The Circular Polarizer has linear polarizer construction plus a built-in "Wave Retardant" to ensure proper exposure. The linear element polarizes the light, and the wave retardant de-polarizes it, and then the beam-splitting meter polarizes the light again for proper exposure. The use of a Linear Polarizer with a beam-splitting meter will result in underexposure.

My question - does the 10D have "beam splitting metering?" I have never come across this phrase before and it looks like it would be a good idea for me to find out now rather than regret it when I buy the wrong kind of filter!

Thanks.
 
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Robertwgross
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      10-12-2004
Mike wrote:
>Hi, I am looking into buying a polarizing filter to use on a Canon 10D. = ...


You want a circular polarizer for a Canon 10D.

---Bob Gross---

 
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GT40
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      10-12-2004
On Tue, 12 Oct 2004 02:18:43 +0100, "Mike" <(E-Mail Removed)>
wrote:

>Hi, I am looking into buying a polarizing filter to use on a Canon 10D.


You need a circular one.
 
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Roger N. Clark (change username to rnclark)
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      10-12-2004
Mike wrote:
> Hi, I am looking into buying a polarizing filter to use on a Canon 10D.
> I've been reading up about this aspect of photography on various
> websites and I came across one which mentions the difference between
> Linear and Circular polarizers. Here's what it says about Circular
> Polarizers:
>
> /CIRCULAR POLARIZER /
> /Provides the same filter effects as a Linear Polarizer, but is designed
> to work with auto focus cameras with beam splitting metering. The
> Circular Polarizer has linear polarizer construction plus a built-in
> "Wave Retardant" to ensure proper exposure. The linear element polarizes
> the light, and the wave retardant de-polarizes it, and then the
> beam-splitting meter polarizes the light again for proper exposure. The
> use of a Linear Polarizer with a beam-splitting meter will result in
> underexposure./
>
> My question - does the 10D have "beam splitting metering?" I have never
> come across this phrase before and it looks like it would be a good idea
> for me to find out now rather than regret it when I buy the wrong kind
> of filter!
>
> Thanks.


What all this means is that the light that reaches the
auto-focus system has been directed there through a beam
splitter: a partially silvered mirror, so some light
passes through, and some light is reflected. A result is
the light becomes partially linearly polarized.
If you put 2 linear polarizers together and rotate them,
the light becomes virtually 100% blocked (0% transmission)
when the polarizers are at 90 degrees. Thus if
you put a linear polarizer on these cameras, depending
on the angle of the polarizer, it can affect autofocus,
or light metering, or both. The circular polarizer
is a linear polarizer plus a 1/4-wave plate which
changes the phase of the linear polarization resulting
in circular polarization, which will not be affected
by the bean splitter in a way that will hurt camera
operation. (I know that last part is technical,
but that's the best I can do in a short paragraph).
You can probably google search for circular polarizer
technical details and get a clearer explanation.
The bottom line is only use a circular polarizer on
autofocus cameras. They cost more because of the added
optical element, the 1/4-wave plate.

Roger

 
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Mike
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      10-12-2004
Thanks to everyone who put me straight on this one


"Roger N. Clark (change username to rnclark)" <(E-Mail Removed)> wrote in
message news:(E-Mail Removed)...
> Mike wrote:
> > Hi, I am looking into buying a polarizing filter to use on a Canon 10D.
> > I've been reading up about this aspect of photography on various
> > websites and I came across one which mentions the difference between
> > Linear and Circular polarizers. Here's what it says about Circular
> > Polarizers:
> >
> > /CIRCULAR POLARIZER /
> > /Provides the same filter effects as a Linear Polarizer, but is designed
> > to work with auto focus cameras with beam splitting metering. The
> > Circular Polarizer has linear polarizer construction plus a built-in
> > "Wave Retardant" to ensure proper exposure. The linear element polarizes
> > the light, and the wave retardant de-polarizes it, and then the
> > beam-splitting meter polarizes the light again for proper exposure. The
> > use of a Linear Polarizer with a beam-splitting meter will result in
> > underexposure./
> >
> > My question - does the 10D have "beam splitting metering?" I have never
> > come across this phrase before and it looks like it would be a good idea
> > for me to find out now rather than regret it when I buy the wrong kind
> > of filter!
> >
> > Thanks.

>
> What all this means is that the light that reaches the
> auto-focus system has been directed there through a beam
> splitter: a partially silvered mirror, so some light
> passes through, and some light is reflected. A result is
> the light becomes partially linearly polarized.
> If you put 2 linear polarizers together and rotate them,
> the light becomes virtually 100% blocked (0% transmission)
> when the polarizers are at 90 degrees. Thus if
> you put a linear polarizer on these cameras, depending
> on the angle of the polarizer, it can affect autofocus,
> or light metering, or both. The circular polarizer
> is a linear polarizer plus a 1/4-wave plate which
> changes the phase of the linear polarization resulting
> in circular polarization, which will not be affected
> by the bean splitter in a way that will hurt camera
> operation. (I know that last part is technical,
> but that's the best I can do in a short paragraph).
> You can probably google search for circular polarizer
> technical details and get a clearer explanation.
> The bottom line is only use a circular polarizer on
> autofocus cameras. They cost more because of the added
> optical element, the 1/4-wave plate.
>
> Roger
>



 
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Justín Käse
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      10-12-2004
In Message-ID:<(E-Mail Removed)> posted on Mon, 11 Oct 2004
20:23:21 -0600, Roger N. Clark (change username to rnclark) wrote:

>The bottom line is only use a circular polarizer on
>autofocus cameras. They cost more because of the added
>optical element, the 1/4-wave plate.


I think the auto exposure reading on my Canon S1 is done by an
evaluation of light hitting the CCD, and therefore not subject to
polarity corruption, but does anyone know if the auto focus is likewise,
such that a LP filter would not adversely affect it?
There was some talk of the auto focus comparing adjacent pixels etc. and
no mention of the light beam being split through some semi transparent
or polarity sensitive arrangement.
--

JK
 
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