Does anyone know of a definitive site with information about the lens coatings used by different manufacturers? I have a variety of lenses, and they have a variety of lens coatings.. Older lenses have yellow or blue coatings, while newer lenses have purple or green. Was the color just a gimmik? Why did they not have perfectly clear coatings? Are some coatings better than others? Which manufacturers skimped on their coatings or had uncoated internal elements?