Stop compensation with square polarizing filter

[Doremus Scudder]

You're overthinking this. First, you can simply take a meter reading through your polarizing filter at whatever orientation you like and base your exposure on that (I do all the time with my spot meter). Second, the amount of difference in overall exposure between the filter in "unpolarized" and "fully polarized" settings may be 1/3-stop or a bit more, not really that much to worry about. People (me included) shot a lot of slide film with TTL cameras and polarizing filters on the lens and did just fine... For negative film there's even more latitude; when in doubt, overexpose a bit.

Best,

Doremus

[Mark Sawyer]

Mark, I agree, instead of reflected light, a better term would be polarized light.

None of the light is polarized before going through the filter, while all of it is after going through the filter, so I'm still confused. Perhaps you meant reflections? Polarizing filters can reduce reflections on the surface of glass, water, etc., but that doesn't mesh with your first post about:

...highlights will be reduced disproportionally compares to the shadows, thereby compressing the dynamic range of the scene.

[reddesert]

Specular reflections are typically highly linearly polarized. Diffuse reflections have very little polarization (see https://en.wikipedia.org/wiki/Specular_reflection and https://en.wikipedia.org/wiki/Diffuse_reflection ). So while all indirect light in a scene is reflected in the sense of bouncing off something, only some of it is polarized enough that a polarizing filter has an effect on it.

To a first approximation, surfaces that make specular reflections also tend to be shiny (ok, the blue sky isn't shiny, or a surface, but it is bright), and polarizers can be used to reduce that. I kind of think most of the people responding agree on the effect of the polarizer but are using different language to describe it.

[Mark Sawyer]

...I kind of think most of the people responding agree on the effect of the polarizer but are using different language to describe it.

I usually go with English...

[Corran]

2 stops!

Almost every polarizer I've used is best with two stops of compensation. Unless you are shooting chromes, if you overexpose a tad bit it's not an issue.

I usually meter the scene with a spotmeter, and but only look at values that are not cut by the polarizer (just look through it and see). In other words, the blue sky is darkened, reflections off water/leaves is darkened, etc.

Bracket the first few times you use it and see what works for you.