In my previous post Fall foliage shooting tips, I have recommended the use of a polarizer and stated the benefits of a polarizer, especially in bright sun light. Here is an good example of using a polarizer for fall foliage shooting.
The first photo was taken without a polarizer and the 2nd with a circular polarizer. For exposure, I used matrix metering and aperture priority mode at f/7.1. The shutter speeds are 1/500s and 1/180s, respectively, for the photo taken without and with a circular polarizer. The Sun is to my left, and the camera-subject direction is perpendicular to the Sun-subject direction, which is the best angle configuration to make the polarizer most effective.
The benefits of polarizer is quite obvious in the photos. The sky is rendered a nice deep blue. The colors of the leaves are more vibrant because of the elimination of the glare and shine. The overall image has more contrast. There are, however, three potential issues you may need to be aware of.
The first is losing shutter speed (assuming you select aperture first for desired depth of field). Polarizer can cut down the light entering the lens by up to two stops. The shutter speed may become so low that blurring will be an issue due to subject movement or camera vibration. Increase the ISO setting if necessary to maintain minimum shutter speed required to capture sharp photos.
The second is noise in blue skies. Due to much lower intensity as the result of filtering by polarizer, the sky is effectively under-exposed significantly in some cases. If you view the images at 100%, you may be able to observe higher level of noise in the sky.
The third potential issue is uneven sky when shooting with a wide angle lens. As mentioned earlier, polarizer works best at specific angle with respect to the Sun and the subject. Since a wide angle lens offers a very large angle of view, not all part of the scene will be filtered by the polarizer with the same effectiveness. The end result is a unnatural-looking sky with very uneven brightness across the frame.
For more information on polarizer:
Keywords: Accessories, Circular polarizer, CPL, polarizer, tips