Lens Type: PhotochromicFogstop is a coating applied to the inside of the lensIt is not smooth but rough – seen through a microscope it looks quite fissuredThis makes it impossible for moisture droplets to form a covering layer| i.eto mist up the lens| impairing visibilityThis could only occur if the humidity level was such that all the fissures are filled with waterBut before this can happen| the stored moisture actually condenses| keeping the lens clear