Hi SM
Here is a link that will explain the characteristics of a polarizing filter.
http://www.digital-photography-school.c ... ng-filters" onclick="window.open(this.href);return false;
Let me add a couple of things.
I do not like putting anything in front of my lens, only if needed.
A cheap piece of glass in front of a $1500 lens doesn't make to much sense, all
it will do is degrade image quality, which is why I spent all that money on the lens
in the first place.
Be careful that you do not over do the darkening effect of the sky, nothing
is uglier than a black-blue sky.
Also on wide angle lens some companies make thinner filters to help reduce
vignetting, but under apertures of 24mm it will still be an issue.
If your into panoramas do not use them because the light fall off at the corners
will ruin your picture, there are ways that you can avoid this but it is not
worth the effort, just shoot without it.
I prefer B&W filters, which are German made, and are of the highest quality, but
I still only use it when needed.