Just like polarized sunglasses, a polarizing lens filter reduces glare from the sunlight that reflects off water and even haze. Some comparison shots taken with and without a polarizer are nothing short of amazing, so given my predilection for landscapes, I recently picked one up and played with it for the first time this weekend.
The filter screws on to the end of the lens (in my case a Pentax DA 35mm Limited) and the outer ring rotates independently so you can adjust the degree of polarization. 90° of rotation is all it takes to go from full polarization to no polarization. You can experience the same effect with polarized sunglasses by turning your head sideways while looking at a body of water.
In the course of figuring out how it worked, I ended up taking some comparison shots without really meaning to. At first the effect was quite subtle, at least until I learned what to look for.
Here’s a fairly pedestrian shot of what looks like a small abandoned boat on the edge of the wetlands around Tubbs Island. The difference between the two versions is pretty dramatic. In the first the water looks blue and reflective, and in the second the water is brown, and you can clearly see the dark marsh grass just below the surface. Also notice how much more vibrant the greens look on the land in the back right of the second. On the other hand, the boat is a tad overexposed. Note: I did no editing to either of these photos besides resizing them.
What surprised me is that the effect of filtering out the reflected light did not always result in a superior picture. I ended up taking two shots of the mudflats after the tide had gone out, and in the one with the polarizer (the second), the contrast between the water and the mud was greatly reduced, to the detriment of the photo. So I took another shot without polarization (the first), which I liked much better. Note: I gently tweaked the contract, saturation, and color balance in the first photo, but not the second.