Excerpt: A CPL is one filter you really must have. Aside from being a protector for your lens, it is valuable in giving you the ability to cut glare from water and glass images. It also will drop 1-2 f-stops, good for outdoor work. This filter is thin and has no vignetting, threads on easily.
Excerpt: Just like a UV filter, everyone who photographs outdoors should have a polarizer. They do cost more, but the effects it produces are so much better. What it does for the photo cannot be done in post processing.