Thanks to the coating of fluorine applied to their lens elements, Nikon's lenses 800mm f/5.6 FL ED VR and 400mm f/2.8 FL ED VR earned the label FL as part of their names. However, what exactly does fluorine coating stand for and why is it so significant?
A two-minute long video recorded by the company Nikon Japan demonstrates the repellent traits which characterize the coating in question after the surface of a lens has been painted and wetted by various substances. In spite of everything, the fluorine coating makes sure that the front element glass becomes a wide waterproof area, which enables much easier removal of any liquids which might spill over the lens surface.
In all probability, getting the front side of the lens smeared by a permanent marker is not such a frequent occurrence, yet even in the situations of that kind, there would be few problems (as it is seen in the video) since this coating precludes the accumulation of material onto the glass and renders lens cleaning considerably easier, without any damage to the lens for that matter.
The news was taken from NIKON.