Polarizer advice

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---

On Tue, 12 Oct 2004 02:18:43 +0100, "Mike"
wrote:

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

You need a circular one.

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

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