Using a Polarizing Filter
I'm sure that this has happened to some of you before -- and if it hasn't, take my word for it, it happens. You're outside on a beautiful sunny day you take what you think is going to be a really nice photo of a field with some nice blue sky, some grass generally a nice picture. When you look at the shot you get a great shot with a white sky and some grass. Generally a poor, boring photograph. This is a time when a Polarizing filter will come in very handy.
The first photograph below, is an image without the benefit of any filtering at all. Please note how dull the sky looks and how washed out the colors appear to be (as you can note in the color of the leaves on the tree and the color of the grass).
The purpose of a polarizing filter is to do a couple of things; 1- reduce or eliminate reflections on glass and water, 2- deepen the blue in a photograph with sky in it, 3- intensify colors.
All of these effects are definitely evident in the photograph below, which is essentially the same image as above, except that a Circular Polarizing filter from Tiffen was added. Please note the bright blue in the sky, which really highlights the clouds, notice how the green in the grass and trees really pops out as does the reddish/maroon in the tree.
There's a few things that you will need to keep in mind when you are using a Polarizing filter. First, get a circular polarizer -- this will allow you to adjust the level of the effect in your picture. Second, the polarizer is designed to change the colors that the camera is capturing. Finally, the polarizer can reduce the amount of light sent into the camera by 2 whole steps. You'll need to experiment with your camera and several shooting situations to get comfortable with what the filter can do for you. Be careful. If you don't intend to make the effect that you will be making, you could definitely alter the appearance of your photograph. The 2 photographs below appear to be VERY different - both the butterfly and the flower are incredibly different when looking at the colors. [I forgot that the filter was on the camera in the photograph that the flowers are deeper purple and the butterfly has a yellowy-purple tinge to the color -- note the whiter color that the butterfly actually was.]