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I can buy a Vivitar brand polarizing filter from Walmart for less than $13, or I can buy a different brand from a photo store in the range of $60 to up over a $100. Instinct tells me that the Vivitar filter will not be as good, but why? Does it have to do with coating or is there another reason? Why should I avoid using the Vivitar brand filter? They seem like a reputable company, no?