Which Polarizer?

Roger N. Clark (change username to rnclark) wrote:
For modern cameras with
AF and and TTL metering, only get circular polarizers

My understanding so far:

Circular polarizer's quarter wave plate makes one wavelength perfectly
circular polarized. Other colors are partially linear polarized. The
amount and orientation of the linear polarization depends on the color
that differ from the quarter wave plate wavelength.

The optical path to the viewfinder is partially polarizing. So it may
interact with the circular polarizer. Depending on the polarizer
orientation, some color may be reduced more than other colors, because
of the above color dependant partial linear polarization of circular
polarizer. So I may see a color change. I want to avoid this color
change caused by the interaction of the viewfinder and the circular
polarizer. I want to be able to depend on the viewfinder to rotate the
polarizer to see the color effect I want that will be recorded on the
sensor. So I choose linear polarizer.

I choose to live with the AE inaccuracy caused by linear polarizer,
because the AE error amount is small. And since I do not use spot
metering, average or matrix metering is not perfect anyway.

AaronW wrote:
Roger N. Clark (change username to rnclark) wrote:

For modern cameras with
AF and and TTL metering, only get circular polarizers


My understanding so far:

Circular polarizer's quarter wave plate makes one wavelength perfectly
circular polarized. Other colors are partially linear polarized. The
amount and orientation of the linear polarization depends on the color
that differ from the quarter wave plate wavelength.

The optical path to the viewfinder is partially polarizing. So it may
interact with the circular polarizer. Depending on the polarizer
orientation, some color may be reduced more than other colors, because
of the above color dependant partial linear polarization of circular
polarizer. So I may see a color change. I want to avoid this color
change caused by the interaction of the viewfinder and the circular
polarizer. I want to be able to depend on the viewfinder to rotate the
polarizer to see the color effect I want that will be recorded on the
sensor. So I choose linear polarizer.

I choose to live with the AE inaccuracy caused by linear polarizer,
because the AE error amount is small. And since I do not use spot
metering, average or matrix metering is not perfect anyway.

Your logic is flawed. The main effect of the circular polarizer
is FIRST as a linear polarizer, so the effect on the scene is the
same whether or not you use a linear or circular polarizer.
The effect of the quarter wave plate in the circular polarizer
does not change the effects of the linear polarizer on the scene.
It does not change the color of the light you perceive, nor what
the camera records (unless your eyes are polarized).
The quarter wave plate is reducing the linearly polarized light
entering the camera (and via the viewfinder, your eye) by
changing it to circular (or elliptically polarized light.
The fact that some colors are not perfectly at
the 1/4-wave plate wavelength is irrelevant regarding
color change on the scene.
It doesn't change the scene's colors; it only changes the
camera's electronic sensors sensitivity to be more accurate.
Use of a linear polarizer simply increases the risk of AF and
or exposure errors.

Roger

Roger N. Clark (change username to rnclark) wrote:
AaronW wrote:
Roger N. Clark (change username to rnclark) wrote:
For modern cameras with
AF and and TTL metering, only get circular polarizers

My understanding so far:

Circular polarizer's quarter wave plate makes one wavelength perfectly
circular polarized. Other colors are partially linear polarized. The
amount and orientation of the linear polarization depends on the color
that differ from the quarter wave plate wavelength.

The optical path to the viewfinder is partially polarizing. So it may
interact with the circular polarizer. Depending on the polarizer
orientation, some color may be reduced more than other colors, because
of the above color dependant partial linear polarization of circular
polarizer. So I may see a color change. I want to avoid this color
change caused by the interaction of the viewfinder and the circular
polarizer. I want to be able to depend on the viewfinder to rotate the
polarizer to see the color effect I want that will be recorded on the
sensor. So I choose linear polarizer.

I choose to live with the AE inaccuracy caused by linear polarizer,
because the AE error amount is small. And since I do not use spot
metering, average or matrix metering is not perfect anyway.

Your logic is flawed. The main effect of the circular polarizer
is FIRST as a linear polarizer, so the effect on the scene is the
same whether or not you use a linear or circular polarizer.

Linear polarizer makes every color linear polarized. The ratio of
polarization and the orientation of polarization is the same for every
color.

The effect of the quarter wave plate in the circular polarizer
does not change the effects of the linear polarizer on the scene.

Circular polarizer does not make every color perfectly circular
polarized. The ratio and orientation of partial linear polarization
changes based on the color wavelength.

It does not change the color of the light you perceive, nor what
the camera records (unless your eyes are polarized).

The viewfinder is partially polarized.

The quarter wave plate is reducing the linearly polarized light
entering the camera (and via the viewfinder, your eye) by
changing it to circular (or elliptically polarized light.
The fact that some colors are not perfectly at
the 1/4-wave plate wavelength is irrelevant regarding
color change on the scene.
It doesn't change the scene's colors

But it changes the color of the viewfinder display, because of the
systematic partial linear polarization based on color wavelength caused
by the quarter wave plate, and the partially polarizing viewfinder.

AaronW wrote:
Roger N. Clark (change username to rnclark) wrote:

AaronW wrote:
I choose to live with the AE inaccuracy caused by linear polarizer,
because the AE error amount is small. And since I do not use spot
metering, average or matrix metering is not perfect anyway.

Your logic is flawed. The main effect of the circular polarizer
is FIRST as a linear polarizer, so the effect on the scene is the
same whether or not you use a linear or circular polarizer.

Linear polarizer makes every color linear polarized. The ratio of
polarization and the orientation of polarization is the same for every
color.

No. It depends on the polarization of light coming from the scene.

The effect of the quarter wave plate in the circular polarizer
does not change the effects of the linear polarizer on the scene.

Circular polarizer does not make every color perfectly circular
polarized.

That does not matter.

The ratio and orientation of partial linear polarization
changes based on the color wavelength.

It has no effect on the scene and how the linear polarizer
in front of the quarter wave plate selectively blocks light
from the scene.

It does not change the color of the light you perceive, nor what
the camera records (unless your eyes are polarized).

The viewfinder is partially polarized.

So the use of a straight linear polarizer maximizes the
problem whereas the quarter wave plate in the circular
polarizer minimizes the problem.

The quarter wave plate is reducing the linearly polarized light
entering the camera (and via the viewfinder, your eye) by
changing it to circular (or elliptically polarized light.
The fact that some colors are not perfectly at
the 1/4-wave plate wavelength is irrelevant regarding
color change on the scene.
It doesn't change the scene's colors

But it changes the color of the viewfinder display, because of the
systematic partial linear polarization based on color wavelength caused
by the quarter wave plate, and the partially polarizing viewfinder.

See the above statement. The polarization of optical components
in the viewfinder, typically a small fraction of an f-stop,
will have small effects. Those effects would be maximized
by a linear polarizer and minimized by a circular polarizer.
The greater issue is not the polarization induced by the
pentaprism, which you would need an instrument to measure,
it is the effect on AF and exposure metering.

Roger

Roger N. Clark (change username to rnclark) wrote:
AaronW wrote:
Roger N. Clark (change username to rnclark) wrote:
AaronW wrote:
I choose to live with the AE inaccuracy caused by linear polarizer,
because the AE error amount is small. And since I do not use spot
metering, average or matrix metering is not perfect anyway.

Your logic is flawed. The main effect of the circular polarizer
is FIRST as a linear polarizer, so the effect on the scene is the
same whether or not you use a linear or circular polarizer.

Linear polarizer makes every color linear polarized. The ratio of
polarization and the orientation of polarization is the same for every
color.

No. It depends on the polarization of light coming from the scene.

I am not discussing the effect of the polarizer on the outside scene.

I am discussing the effect of the partially polarized viewfinder on the
light behind the polarizer.

The effect of the quarter wave plate in the circular polarizer
does not change the effects of the linear polarizer on the scene.

Circular polarizer does not make every color perfectly circular
polarized.

That does not matter.

That is the most important basis of the discussion.

The ratio and orientation of partial linear polarization
changes based on the color wavelength.

It has no effect on the scene and how the linear polarizer
in front of the quarter wave plate selectively blocks light
from the scene.

Again, I am not discussing the effect of the polarizer on the outside
scene. I am discussing the effect of the partially polarized viewfinder
on the light behind the polarizer.

It does not change the color of the light you perceive, nor what
the camera records (unless your eyes are polarized).

The viewfinder is partially polarized.

So the use of a straight linear polarizer maximizes the
problem whereas the quarter wave plate in the circular
polarizer minimizes the problem.

With a linear polarizer, every color will be darker (or not) by the
same amount. You think that is the problem. For me, this is not the
problem, since there is no color change, only brightness change. My
eyes are not that sensitive to slight brightness change. But they are
sensitive to slight color change.

With a circular polarizer, some color will be darker than other colors.
Which color is darker depends on the relative orientation of the
circular polarizer and the partially polarizing viewfinder. So as you
rotate the circular polarizer, the viewfinder will show different
color. To control the variables better, keep the circular polarizer
stationary, so its effect on the outside scene is fixed. Then you
rotate the camera viewfinder, the color shown in the viewfinder will
change. This is the problem that linear polarizer does not have.

The quarter wave plate is reducing the linearly polarized light
entering the camera (and via the viewfinder, your eye) by
changing it to circular (or elliptically polarized light.
The fact that some colors are not perfectly at
the 1/4-wave plate wavelength is irrelevant regarding
color change on the scene.
It doesn't change the scene's colors

But it changes the color of the viewfinder display, because of the
systematic partial linear polarization based on color wavelength caused
by the quarter wave plate, and the partially polarizing viewfinder.

AaronW wrote:

Roger N. Clark (change username to rnclark) wrote:
AaronW wrote:
Roger N. Clark (change username to rnclark) wrote:
AaronW wrote:
I choose to live with the AE inaccuracy caused by linear polarizer,
because the AE error amount is small. And since I do not use spot
metering, average or matrix metering is not perfect anyway.

Your logic is flawed. The main effect of the circular polarizer
is FIRST as a linear polarizer, so the effect on the scene is the
same whether or not you use a linear or circular polarizer.

Linear polarizer makes every color linear polarized. The ratio of
polarization and the orientation of polarization is the same for every
color.

No. It depends on the polarization of light coming from the scene.

I am not discussing the effect of the polarizer on the outside scene.

I am discussing the effect of the partially polarized viewfinder on the
light behind the polarizer.

The effect of the quarter wave plate in the circular polarizer
does not change the effects of the linear polarizer on the scene.

Circular polarizer does not make every color perfectly circular
polarized.

That does not matter.

That is the most important basis of the discussion.

The ratio and orientation of partial linear polarization
changes based on the color wavelength.

It has no effect on the scene and how the linear polarizer
in front of the quarter wave plate selectively blocks light
from the scene.

Again, I am not discussing the effect of the polarizer on the outside
scene. I am discussing the effect of the partially polarized viewfinder
on the light behind the polarizer.

It does not change the color of the light you perceive, nor what
the camera records (unless your eyes are polarized).

The viewfinder is partially polarized.

So the use of a straight linear polarizer maximizes the
problem whereas the quarter wave plate in the circular
polarizer minimizes the problem.

With a linear polarizer, every color will be darker (or not) by the
same amount. You think that is the problem. For me, this is not the
problem, since there is no color change, only brightness change. My
eyes are not that sensitive to slight brightness change. But they are
sensitive to slight color change.

With a circular polarizer, some color will be darker than other colors.
Which color is darker depends on the relative orientation of the
circular polarizer and the partially polarizing viewfinder. So as you
rotate the circular polarizer, the viewfinder will show different
color. To control the variables better, keep the circular polarizer
stationary, so its effect on the outside scene is fixed. Then you
rotate the camera viewfinder, the color shown in the viewfinder will
change. This is the problem that linear polarizer does not have.

Uh, why do you care about color shifts showing up in the viewfinder?

The quarter wave plate is reducing the linearly polarized light
entering the camera (and via the viewfinder, your eye) by
changing it to circular (or elliptically polarized light.
The fact that some colors are not perfectly at
the 1/4-wave plate wavelength is irrelevant regarding
color change on the scene.
It doesn't change the scene's colors

But it changes the color of the viewfinder display, because of the
systematic partial linear polarization based on color wavelength caused
by the quarter wave plate, and the partially polarizing viewfinder.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

J. Clarke wrote:
AaronW wrote:
Roger N. Clark (change username to rnclark) wrote:
AaronW wrote:
Roger N. Clark (change username to rnclark) wrote:
AaronW wrote:
I choose to live with the AE inaccuracy caused by linear polarizer,
because the AE error amount is small. And since I do not use spot
metering, average or matrix metering is not perfect anyway.

Your logic is flawed. The main effect of the circular polarizer
is FIRST as a linear polarizer, so the effect on the scene is the
same whether or not you use a linear or circular polarizer.

Linear polarizer makes every color linear polarized. The ratio of
polarization and the orientation of polarization is the same for every
color.

No. It depends on the polarization of light coming from the scene.

I am not discussing the effect of the polarizer on the outside scene.

I am discussing the effect of the partially polarized viewfinder on the
light behind the polarizer.

The effect of the quarter wave plate in the circular polarizer
does not change the effects of the linear polarizer on the scene.

Circular polarizer does not make every color perfectly circular
polarized.

That does not matter.

That is the most important basis of the discussion.

The ratio and orientation of partial linear polarization
changes based on the color wavelength.

It has no effect on the scene and how the linear polarizer
in front of the quarter wave plate selectively blocks light
from the scene.

Again, I am not discussing the effect of the polarizer on the outside
scene. I am discussing the effect of the partially polarized viewfinder
on the light behind the polarizer.

It does not change the color of the light you perceive, nor what
the camera records (unless your eyes are polarized).

The viewfinder is partially polarized.

So the use of a straight linear polarizer maximizes the
problem whereas the quarter wave plate in the circular
polarizer minimizes the problem.

With a linear polarizer, every color will be darker (or not) by the
same amount. You think that is the problem. For me, this is not the
problem, since there is no color change, only brightness change. My
eyes are not that sensitive to slight brightness change. But they are
sensitive to slight color change.

With a circular polarizer, some color will be darker than other colors.
Which color is darker depends on the relative orientation of the
circular polarizer and the partially polarizing viewfinder. So as you
rotate the circular polarizer, the viewfinder will show different
color. To control the variables better, keep the circular polarizer
stationary, so its effect on the outside scene is fixed. Then you
rotate the camera viewfinder, the color shown in the viewfinder will
change. This is the problem that linear polarizer does not have.

Uh, why do you care about color shifts showing up in the viewfinder?

Because I rotate the polarizer, while looking into the viewfinder, in
search for the color effect I like. If the color shown in the
viewfinder is not the same as the color that will be captured by the
sensor, then it is a problem. This is the problem with circular
polarizer that I can avoid by using linear polarizer instead.

In article , "Roger N. Clark (change
username to rnclark)" writes
AaronW wrote:
J. Clarke wrote:

Uh, why do you care about color shifts showing up in the viewfinder?
Because I rotate the polarizer, while looking into the viewfinder,
in
search for the color effect I like. If the color shown in the
viewfinder is not the same as the color that will be captured by the
sensor, then it is a problem. This is the problem with circular
polarizer that I can avoid by using linear polarizer instead.

Q: Which produces a greater change in transmitted color:
a) crossed linear polarizers?
b) two circular polarizers?
c) circular polarizer followed by a linear polarizer?

A: a. If you try this experiment and find a larger
shift with b or c, then your circular polarizers are crap.

Roger

Roger,

I'm afraid you are quite wrong here. The CPs in (b) and (c) *must*
create more colour variation than the two LPs in (a), simply from the
physics of how CPs work.

A pair of ideal LPs will produce no visible colour variation (and do not
do so in the ones I have tested) though the strong intensity variation
makes it hard to observe perfectly.

A CP followed by any polariser (CP or LP) will show slight colour
variations, since only light of the wavelength for which it has a
retardation of one quarter of a wavelength will be perfectly circularly
polarised. Light of other wavelengths will remain (slightly)
elliptically polarised and will show some variation in intensity as the
two filters are rotated. Try it and you will see it is so.

Where I differ from Aaron is whether this is an effect of any
significance in use, and whether it outweighs the effect on metering and
AF systems of using a linear polariser. Aaron thinks the polarisation of
the reflex mirror is enough to give him an unacceptable level of colour
change in the viewfinder, but does not mind the risk of errors in
metering etc. I take the opposite view on both points (the polarisation
effect of the mirror is smaller than the use of a second polarising
filter). What cannot be denied, however, is that the effect does exist
when using two filters.

David
--
David Littlewood

AaronW wrote:
J. Clarke wrote:

Uh, why do you care about color shifts showing up in the viewfinder?


Because I rotate the polarizer, while looking into the viewfinder, in
search for the color effect I like. If the color shown in the
viewfinder is not the same as the color that will be captured by the
sensor, then it is a problem. This is the problem with circular
polarizer that I can avoid by using linear polarizer instead.

Q: Which produces a greater change in transmitted color:
a) crossed linear polarizers?
b) two circular polarizers?
c) circular polarizer followed by a linear polarizer?

A: a. If you try this experiment and find a larger
shift with b or c, then your circular polarizers are crap.

Roger

Roger N. Clark (change username to rnclark) wrote:
AaronW wrote:
J. Clarke wrote:
Uh, why do you care about color shifts showing up in the viewfinder?

Because I rotate the polarizer, while looking into the viewfinder, in
search for the color effect I like. If the color shown in the
viewfinder is not the same as the color that will be captured by the
sensor, then it is a problem. This is the problem with circular
polarizer that I can avoid by using linear polarizer instead.

Q: Which produces a greater change in transmitted color:
a) crossed linear polarizers?
b) two circular polarizers?
c) circular polarizer followed by a linear polarizer?

A: a. If you try this experiment and find a larger
shift with b or c, then your circular polarizers are crap.

We went through this before. My polarizers are B+W brand.

If I stack two polarizers together, if the front is a circular
polarizer, I see color change. If the front is a linear polarizer, I
see brightness change, but no color change. Other people have confirmed
this observation with high quality polarizers.

And the theory discussed in this thread supports this observation.