The Polarizing camera filter is one of the most essential pieces of equipment for any landscape photographer.
It is basically a piece of dark glass that fits onto the front of your lens and is an effective way to reduce the luminance range of a scene. This makes blue skies appear darker than they really are and reduces glare from smooth non-metallic surfaces such as glass, water or gloss paint.
Using Polarizing Filters
This Video from DLSRTIPS.COM explains how to use polarizing filters and in what situations they are best used.
Polarizing Filter Tips
When buying a polarizing filter make sure you buy a circular type rather than a linear filter. The Linear types are cheaper but can render auto focus and some metering systems inaccurate.
Make sure you buy a filter that will fit your lens size. Check the thread size of your lens.
With the filter fitted to your lens turn the filter to increase or decrease the polarizing effect. You may have to take several shots to see the results in your viewfinder.
Set the white balance of your DLSR to Daylight so that the camera does not try to over ride the filter effect.