Introducción sobre el uso del polarizador circular

Easy to follow introduction to the proper use of circular polarizing filters-
One thing to note is that some cheaper lenses rotate the end of the lens barrel when autofocusing, and some do not. If you carefully set your polarizer, then autofocus, you might have to reset the polarizer.

Fuente: http://betterdigitalphotography.blogspot.com/2011/01/how-to-use-circular-polarizing-filter.html