Recently wanted to get a Hoya HMC UV filter. Upon close inspection, noticed that there were a few small bluish specs in the coating of the glass. These are not fungus, dirt or stains, because even after rubbing with a lint free cloth, and using a lens cleaning pen, it still doesn't come off.
Also, around the part where the glass meets the mounting ring, there is this strip which I think helps to maintain the glass fixed onto the ring, as well as sealing the gap. This strip was uneven, and had a gap of around 2mm between each end.
I know Hoya filters are supposed to be good, but with these characteristics?
Another thing about filters is, if I just want a lens protecting filter, would a cheaper filter like vitacon do just as well? Would the optical quality of the lens be adversely affected by the use of a cheap filter? Even if it's just a UV filter?
I just got a Sigma 15-30mm (Filter size 82mm) and a Nikkor AFD 80-200mm F2.8 (77mm). I wanted to get Hoyas, UV & CIRC Polars for both lenses. But after seeing the Hoya's problems, I got cheaper vitacons instead.