Strength of linear vs. circular polarizer

[inthesouthofireland]

Hi All,

Does anyone here own both a linear and a circular polarizer from the same manufacturer?
If so, is the strength of the polarizing effect the same with both filters or is it stronger with the linear one?

Many thanks!

[Slobodan Blagojevic]

There should be no visual or strength difference in the effect. The only difference is in how they achieve that effect.

[inthesouthofireland]

I have a linear and a circular polarizer here, but they are from different manufacturers.
The linear polarizer is stronger - a LOT stronger. Maybe this explains my question better...

[frugal]

I wouldn't worry too much about it unless you're using an extremely old camera that can actually use the linear polarizer without fouling up its metering and/or AF.

[Slobodan Blagojevic]

I have a linear and a circular polarizer here, but they are from different manufacturers.
The linear polarizer is stronger - a LOT stronger. Maybe this explains my question better...

Can you explain what do you mean by "a LOT stronger"? Or, even better, illustrate it?

[schrodingerscat]

I wouldn't worry too much about it unless you're using an extremely old camera that can actually use the linear polarizer without fouling up its metering and/or AF.

Yes, if using linear polarizers, remember to use manual focus and exposure.

[PeterAit]

Hi All,

Does anyone here own both a linear and a circular polarizer from the same manufacturer?
If so, is the strength of the polarizing effect the same with both filters or is it stronger with the linear one?

Many thanks!

If I recall correctly, a circular polarizer (dumb name) is nothing more than a lineal polarizer with a quarter wave plate added to partially undo the polarization so that autofocus can work. Thus, the circular would be less strong in effect than the linear.

[pfigen]

I did a shot last week with a Canon 35mm 1.4 with both a Tiffen linear polarizer that I've had for at least twenty years AND a .9 (3 stop) ND filter and was shocked to see the lens still autofocusing on a 1DsMKIII on the center point. Not that I'd recommend it or that it was accurate, but only that it was focusing until I switched to manual focus.

[grzybu]

Yes, if using linear polarizers, remember to use manual focus and exposure.

I was using linear polarizer with old Minolta D7D without any problems with AF or exposure metering.
The same situation with Panasonic G1, but there are no mirrors and AF is contrast based so it's different story.
Some cameras can handle linear polarizers some not so good.

[EricV]

If I recall correctly, a circular polarizer (dumb name) is nothing more than a linear polarizer with a quarter wave plate added to partially undo the polarization so that autofocus can work. Thus, the circular would be less strong in effect than the linear.

  The first statement is correct, but the conclusion is wrong.  The first linear polarizer determines the strength of the effect, and the following quarter wave plate does not dilute this strength (light blocked by the polarizer is gone forever).

[PeterAit]

  The first statement is correct, but the conclusion is wrong.  The first linear polarizer determines the strength of the effect, and the following quarter wave plate does not dilute this strength (light blocked by the polarizer is gone forever).

Thanks for the clarification.

[AJSJones]

Circular polarization isn't such a dumb name - the plane of polarization goes in a circle as the wave moves forward.
I don't think metering is sensitive to the phase of the light, so it should not be influenced by the choice of circular over linear..

[frugal]

Circular polarization isn't such a dumb name - the plane of polarization goes in a circle as the wave moves forward.
I don't think metering is sensitive to the phase of the light, so it should not be influenced by the choice of circular over linear..

The issue is if you're using a camera with a partially silvered mirror (like just about any SLR made in the last 20 years or so). A linear polarizer will interfere with the mirror which can foul up AF or metering.

[AJSJones]

The issue is if you're using a camera with a partially silvered mirror (like just about any SLR made in the last 20 years or so). A linear polarizer will interfere with the mirror which can foul up AF or metering.

I understand the phase-dependent AF might get fooled by messing with the polarization/phases of the incoming photons but how does the phase affect how much total light gets through a half-silvered mirror - onto the (phase-insensitive) meter segments?

[Bart_van_der_Wolf]

I understand the phase-dependent AF might get fooled by messing with the polarization/phases of the incoming photons but how does the phase affect how much total light gets through a half-silvered mirror - onto the (phase-insensitive) meter segments?

The mirror surface polarizes the light in one plane. If that plane happens to be (partially) crossed relative to the polarizing filter, then the metering sensor will detect the wrong intensity.

Cheers,
Bart

[inthesouthofireland]

Given that a circular polarizer is just a linear polarizer plus a quarter wave plate, it seems logigal to assume that the strength of both should be the same. I was an inch away from buying a new circular one, but did some more googling just beforehand and came across a test of circular polarizers.

The really fascinating bit here is the fact that the best polarizer of the whole line-up turned out to be a linear one which was mislabeld. :-)
The measured extinction coefficient of the linear polarizer is clearly better than that of the circular polarizer from the same manufacturer.

Theory vs. practice...