Hoya circular polarizer on A99 do or don't

Don't buy any adapter rings!  Get the appropriate thread sized filters.  Are you intending to use for better colour and shadow reduction, otherwise it's a waste of money, though a CPL filter will enhance an image quite a lot.  Not much point buying a filter for a lens that isn't going to be used much, so be selective before you decide.

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Mark @ Sonolta * Photography