Lens coating for photographic lenses was developed to improve lens speed & light transmission by reducing light loss from scatter and internal reflections. Uncoated lenses tend to be less contrasty, getting milkier when the camera is pointed at a bright sky, for example. Lens coating was invented in the mid 1930's -- Gregg Toland was one of the first cinematographers to use coated lenses extensively. So I'm not sure it is historically accurate for "Saving Private Ryan" to use uncoated lenses since most WW2 photography probably would have used coated lenses, but certainly the lenses back then were still less contrasty than modern lenses. The look of older lenses is subtle and yet immediately effective in making something look like period photography.