Why are modern spectacles impossible to clean properly with anything other than a special cleaning cloth?
Whenever I try to get rid of even a small surface mark using a handkerchief, I end up with seemingly permanent multicoloured smears that can’t be removed. • The lenses of some modern spectacles, like those of many cameras, have a special anti-glare coating that reduces reflections at the lens surface. This works by creating a second reflection at the coating surface that interferes with, and cancels out, the original reflection. To create the desired interference, the coating thickness must be just right. Unfortunately, any attempt to rub a greasy spot off a lens turns it into an additional coating of varying thickness, which produces the multicoloured reflections seen. Even worse, handkerchiefs are often laundered with a “softener” that leaves grease in the fabric, and makes things worse. The lens cloths made for cleaning absorb the grease instead of spreading it.
