Note: I was provided this product free of charge by the manufacturer but no attempt has been made to influence my review.Tested on a Sigma 50-500 lens with an 86mm diameter, this filter fits nicely (although the thread is narrow so do it slowly to avoid cross threading). Tested in comparison to a Hoya UV filter I currently use I saw no noticeable difference in the photos produced. It is good value for money, but I did notice even in my brief testing that the paint did come off a little bit... I don't know how much of an issue this is, as I tend to keep UV filters on lenses as a means of protecting them.This does present one issue though with this filter. As described in its name, it is slim. Given my main reason for having the filter on a lens (especially a quite expensive lens) is to protect the lens if I accidentally knock it or drop it, I have reservations about something so slim... it just doesn't protect that much. I have a couple of lenses which have had minor accidents which are carried about with bent UV filters on the end, and I'm not so sure this one would help in such a situation.As a filter in its own right, I'm happy with this product.. but I'm not so sure from the perspective of a filter to protect the lens itself.