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"absorbs the ultraviolet rays which often make outdoor photographs hazy and indistinct."
Hmm, i'm really not that sure that these UV filters do cut out all that much UV light, i'm sure it is more of a marketing gimmick rather than a genuine problem as never have I experienced any UV 'haze' even when shooting with telephoto lenses, I think the problem of UV affecting images is going back to the days of film cameras and uncoated lenses- the filter market is really struggling to thrive when most people do filters digitally these days, so filter manufactures and camera store shop staff try and scare you into buying their products.
I use these filters mainly for protection and to complete the weather sealing on canon L series lenses. The build quality is ok, but not fantastic- the glass actually shakes around a little until you put it onto the camera- this is fine and I don't expect it to fail but it doesnt inspire confidence. In terms of IQ i've not noticed any drop in sharpness with a 70-200 2.8, and flare hasn't been a problem either (although there are times where it could be a problem, so if you need absolutely perfect flare resistance you might have to spend a little more)
Hoya are a generally good brand, not super high end like zeiss or heliopan but noticeably better than the no-brand and Chinese imports. The price of these hoya filters is so low its not worth thinking about trying to get something cheaper, unless you really need the high end filters, then these hoya's are plenty good enough for L glass