How is this effect applied across the image? Does unpolarized go towards the one color and polarized the other?
I've dicked around with using LR's duotone controls on color photos but I'm assuming this is not the same thing.
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The filter only operates on polarized light in the blue or gold wavelengths (depends on rotation of filter). It does not affect non-polarized light, and the effect is not easily done in PP, however, it does have a magenta cast so you will need to shoot RAW and WB in order to arrive at a proper image. Also, if you stack a ND then the effect is magnified.
The Point Pleasant Sunset image from my post above is a good example of the manner in which the filter operates on a properly WB'd image... note the gold within the foliage in the foreground and the beam of light reflected on the ocean.
If the scene has multiple polarized light sources then it is possible to get both a blue and a gold effect within the same image due to the different angles of the polarized light. Note the blue that creeped in at the top and right facing rocks within the Golden Rocks image due to the different angles. Also, if you screw the image up by dialing in too much gold or blue, it is very difficult to recover the image (lots of time with LAB curves, masking, etc.).
I have attached a series of three rock images: blue with ND, gold with ND, and Gold with ND that has been desaturated (dialed in way too much gold).
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