Two shots, seconds apart; top without polarizer, bottom with polarizer.
(D70 with 18-70mm @18mm f/7.1 1/400s and 1/100s respectively)
Shown resized but otherwise unprocessed with Photoshop CS Luminosity histograms to the right of each image.
The histograms are highlighted to show the dynamic range used.
No polarizer uses levels 7 to 234; 228 levels.
With polarizer uses levels 6 to 216; 211 levels.
With polarizer uses about 1/3EV less dynamic range in this case.
(I examined the linear raw data, not shown, to compute this.)
Also note that the right hand side of the luminance is "better behaved" with the polarizer.

Bill

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I guess the point you're trying to make is that a polarizer can help you keep from blowing out the highlights when those highlights are polarized light, like reflections. That's worth keeping in mind.

-- Jon

The reflections without the Pol are strongly polarized (and degrade the image IMO).

With the Pol the Pol light from the reflections (and the sky) is taken out.
This adds detail particularly in the water reflections and there is better saturation.
There are also fewer highlights getting through the filter so the luminosity mix is changed.

Strongly pol light often also prevents foliage colours getting through.
You can see much more green detail on the trees above the far bank with the Pol in place - and IMO this helps make the pol image look better.

Whether or not the Pol reduces dynamic range is IMO a diversion.

The main point to me is in this example the Pol produces a much better picture.
Photography IMO is much more about making better pictures than luminosity readouts.

Len Shepherd.

Dope slap

Bob (and Len) were right. The dynamic range is not reduced.
That would have required that 100% of the brightest portion of the unpolarzied image to have been composed of polarized light.
(The high end was knocked down considerably, but not entirely.)

This also jives with Circular polarizer transmittance which was inspired by Guy in post#4.

The photo with polarizer appeared to have a 1/3EV drop in dynamic range.
But that was just the difference between the polarizer transmittance penalty of 1 2/3EV and the exposure difference of 2EV.

Thanks for pushing me guys, believe it or not I'm here to learn too!

Bill

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