Circular Polarizers - Part 1
So I had an eye opening experience last weekend. I'm out walking with my faithful photo assistant Abby (my Jack Russell Terrier) and I decided the day was going to be a worthless photo-outing since the sun was out and there was not a cloud in the sky. Instead of wasting the day, I decided to have some fun experimenting with my circular polarizer. One of the functions of a circular polarizer is to make skies more blue when it is rotated just the right way. Another function is to reduce/eliminate reflections on glass/water/foliage. On this day, my intent was just to see what I could do with these big blue skies that were ruining the potential for getting a good "melancholy" image. So I shot off a couple of frames with the polarizer turned a bit each time. Turning a circular polarizer changes the intensity of it's effect on the scene.
Here are my results:
Wow! What a difference. This little circular polarizer works some kind of magic. It has made the colors more saturated. But it has also done something else, which I consider even more valuable. Let me explain.
When I look at the two images above, one seems to have a higher dynamic range. How can image two seem to have a higher dynamic range? If you look at it, the trees and power lines are less of a silhouette and have more color than in the first image. The bricks on the house are showing detail that is lost in the shadows of the first image. You see much less blocked up (blacked out) shadow area in the second image. Just look at the tree on the right side of the image to see what I mean.
What has happened here is that by darkening the blue sky which is dominating the frame, the polarizer forced me to use a slower shutter speed. On the first image I think I was at 1/180 second and the second image, closer to 1/60 second. By darkening just the sky, the polarizer is working much like a Graduated Neutral Density filter would do. Except with a GND filter, you are usually just darkening a general area of an overall image. The Polarizer is selectively choosing to darken just the sky in this image. What that then allows me to do is use a slower shutter speed and give more exposure to the shadow areas resulting in more detail and color in the image.
It's like using HDR software without the hassle and artificial effects that the software produces. All of a sudden, I'm very curious about how this circular polarizer may change my attitude toward sunny days. I plan to do a more controlled study, with and without the polarizer (the two images here both had the polarizer on the lens) and also compare the results to something I might be able to do using software after the fact. In addition, I plan to do some work on how the polarizer reduces reflections, but that seems less important to me at the moment than the possibility of creating HDR in-camera with just one image.









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