I'm assuming there's no UV filter or anything on it that might be causing a problem. So take it off the camera, use your finger to open up the aperture blades, and shine a flashlight through it, in both directions… see what it looks like inside - dust, etc… then check it from angles. The coating should be reducing reflections, so it shouldn't be too shiny, but if the coating has been damaged it should be obvious. Some people are a little too vigorous in their cleaning. Might be a problem with the rear element, too, not just the front. That lens has such tiny elements (at least, my 40xs does and I think they're the same) that it might be difficult to keep clean properly. I've had a few pairs of glasses where I damaged the antireflective coating. I'm more careful with lenses. (and the last pair of glasses I bought I opted for mineral glass, no coatings at all (UV protection is built in somehow).
---------- Post added 04-18-14 at 01:13 PM ----------
Originally posted by bsamcash Thanks for the reply.
What exactly would I be looking for? I held the blades open and shined a light through and saw dust. What else should I be looking for?
Though much of what he posts is questionable, this one is pretty solid.
The Flashlight Test