So I went to the local photo store looking for a filter for my Mamiya RZ67. I wanted a polarizer, and was shocked when the storekeeper told me the only filter he sold was 250 EUR. He told me that if I had a 77mm lens, it must be a high quality lens, and I shouldn't buy anything but the best filters for such a lens, because otherwise sharpness and contrast will suffer. Is there any truth to that? I bought my mamiya second hand and literally the filter would cost more then I paid for the mamiya. And I do love the mamiya and the pictures she takes, but 250 EUR seems realllly expensive. How much sharpness would I really use if I went with, say, a cheap square filter system?