Adwords imprecision

I was told once that one of the best sources of revenue for the post office is over-franking. And I suspect a similar thing is true for Google Adwords. Behold: I made a search for "ZF lenses", which are made by Zeiss for Nikon cameras. (Manual focus high-quality lenses.) And not one, but three spectacles stores put their ad on top, because apparently their key words settings make them pop up whenever anybody search for "lenses" no matter what kind of lenses it is. What a waste, the wonderful thing about Adwords is exactly that you can be precise about targeting your public.