Originally posted by Eder Hi bdery thanks for you answer. Pentax user's manual says that when using autofocus, lens do not rotate. so this means that i need a non-rotating polarizer filter when i use autofocus?
You got this backward a bit.
Independent of any filter, a lens's front element might rotate or not, depending on the design of the lens. Cheaper lenses will often have a rotating front element.
Now most filters are fixed (UV, ND, coloured, etc). However, some filter types, among them polarizers, have a rotating element. This is part of how they operate, not related to their quality or anything else. Again taking a polarizer as example, it needs to rotate to adjust its effect in relation to surrounding conditions.
Now, imagine you set your polarizer by rotating it, then you focus your lens and the front element rotates, messing up with how you adjusted your polarizer. That,s annoying... This is why most manufacturers will see "non rotating front elements" as perks and will list that feature on spec sheets.
That's all there is to it.