Since writing “A Few Polarization-Filter Examples” several years ago, I've been meaning to do a post on a polarization filter's effects when shooting fall foliage. Over the years I've mentioned some effect or other of a polarization filer on my blog (such as here, here, and here), but I'm only now getting to filling in a huge deficiency of my 2007 post on making the best of bright light in fall-color photography by demonstrating how useful a polarizing filter can be when shooting foliage.
While at the Yoshiminedera Temple south of Kyoto during various trips last year, I did something I do often: snapped some pairs of shots with and without a polarization filter. Today I'm doing something I don't often do: actually making use of them. As I mentioned last year in “Photo Shoot Among the Fall Colors at Shouzan”, I thought I'd get around to this post soon, but a year later, finally, here we are.
As you can see in these examples, colors can be much richer, and shiny reflections reduced. Before I talk about why, I should mention a bit about how I made these shots....
First, I should have used a tripod, and perhaps sometime I'll go to that trouble, but these were all snapped freehand. Most often I'd find the rotational angle of the polarizer filter that maximized the effect, then snap a shot, quickly rotate it 90 degrees while trying not to move, and snap another shot. Later in Lightroom I attempted to compensate for slight camera movement by adjust one crop or the other, but otherwise each pair has identical, default “just loaded into Lightroom” processing. (I did subject the photos to my standard treatment via my bulk-develop plugin, but I don't think any of these photos would have been affected by it.)
So, to be clear, this means that the “without” is not really “without a filter”, but “with the filter at its least impact”.
So, what's happening when we use a polarizing filter? If light is polarized for whatever reason, a polarizing filter blocks most of the light, at least when the filter is rotated to “align” to the polarized light. Most light is not polarized, so the filter does not block much of that light, but some kinds of light are strongly polarized, and those can be strongly blocked while, again, leaving other kinds of light mostly alone.
Strong reflections from the sun on the leaves in the photo above cause the whole “Without Polarizer” version to be washed out a bit, and each individual area of reflection is washed out considerably, towards pure white. But for whatever reason, those reflections are mostly polarized, so when I use a polarization filter and rotate it to maximize the filtering of the reflections, the overall dynamic range of the scene is reduced to a sweeter spot for the camera sensor, resulting in richer colors and a more aesthetically-pleasing result. The non-polarized light is still there so we still see the leaves, but the blinding reflections are greatly reduced. It's the same effect for your eyes when you put on a pair of polarized sun glasses.
(By the way, a polarizing filter would be better called a “polarized-light filter” because it filters that kind of light; the term “polarizing filter” sounds to me as if it somehow turns non-polarized light into polarized light.)
Light from a blue sky is often polarized, though it depends on the time of day and the direction you're facing relative to the sun. In this case, a polarizing filter tends to bring down the overall brightness of the sky relative to the rest of the scene, compressing the dynamic range, which allows a deeper blue.
You can read on Wikipedia all about polarized light if you're interested in the physics behind it.
Not all scenes are affected by a polarization filter. You can test the effect by holding the filter to your eye (have the part that would face the lens facing your eye) and rotating... you'll either see the effect clearly, or you won't. I've some experience using these under my belt, but I'm still not very good at predicting which lights will be polarized, and the overall effect of using a filter on them. But luckily, it's easy to test and experiment while out and about, so I generally keep a filter or two in my camera bag.
By the way, as a good test of your filter, try viewing a smartphone screen through the filter and rotating... my old iPhone 3G's screen becomes perfectly black at certain angles, though my new iPhone 4s's screen merely shifts colors, a technical advance sure to be a boon to sunglasses-wearing phone users.
Anyway,not all scenes look better with the filter. Both versions of the following photo are uninteresting:
Consider the water reflections in “Snowy Gardens of the Heian Shrine”... removing them would destroy those shots, so it was definitely a situation where one would not want a polarization filter.
Some more examples follow...