I took a rare solo ride through the Kern River Canyon (Hwy 178) this afternoon in search of some photos. What I ended up with was an object lesson in the many benefits of using a polarizing filter. If you're not familiar with them, polarizers are adjustable, dark filters that adjust the incoming light. They work best when photographing a 90 degree angle to the sun.
First and foremost, a polarizing filter can be used to bring out the blue in the sky.
I'm pleased to note that the self-cleaning sensor on my Canon 40D seems to be working quite well.
A second benefit of a polarizing filter is its ability to saturate the image by reducing or eliminating reflections, in this case, on the water's surface.
Kern River taken at 17mm (28mm equivalent)
Kern River taken at 85mm (135mm equivalent)
The third benefit of a polarizing filter is that it functions also as a neutral density filter. The dark filter reduces the amount of incoming light by two f-stops. This is true of all polarizers, though specific neutral density filters can be purchased in 4, 8, or more stops of density.
Why would anyone want this? Sometimes you want to shoot something with a low shutter speed in bright daylight. You can lower the ISO to 100, and you can stop the lens down to f/32, but sometimes you need a little bit more. That's where an ND filter, or in this case, a PL filter, comes in handy.
1.3 secs. @ f/32
2 secs. @ f/32
8/10 sec. @ f/29
1/2 sec. @ f/29
It should go without saying the four photos above were all taken on a sturdy tripod. A darker ND filter would have resulted in slower shutter speeds and a more "painterly" quality to the water.
Click on any image for EXIF info.