i got a few filters today and i am very new to the photography world. so i had the guy at ritz help me he told me to buy a polarizer and a circular polarizer. he said the cir. pol. is for auto focus and the regular pol. is for manual. my question is what is the difference and if i had the cir. pol. on and switch to manual focus do i have to switch the filter too. and btw i have the a100