You can unscrew the steel bezel and carefully pry off the optics to blow them out, but you’ll still probably see some dust inside the optics. I’ve had a couple of optics based lights now including the D4s, and they all show some form of dust or another inside the optics once lit, it’s something where unless you’re in a vacuum assembling the optics, you’re going to see particles in the optics, because they’re like magnifying glasses.