Subwavelength Structure Coating (SWC)
Light waves that can be seen are thinner than the coatings on the surface of lenses. A technique called "evaporated film coating" is used by Canon to cover the lens's surface with a very thin layer that makes it less reflective and lets more light through. This keeps lens flare and ghosting to a minimum. On the other hand, evaporated film coatings lose some of their anti-reflective properties as the angle at which light enters and leaves the material gets sharper. This means that to get even better imaging results, we need to find even better ways to stop light from reflecting. Canon was unable to make any more progress on developing new optical arrays because evaporated film coating had been used to its full potential.
SWC, or Subwavelength Structure Coating, is the name of the new technology that raised the level of anti-reflective film coatings. With this technology, lens flare and ghosting can be controlled even on surfaces of the lens that evaporated film coating couldn't stop before. The principle behind SWC that stops reflections is based on the refractive index changing all the time. There is a difference between the refractive index of glass and air, which is what makes the lens surface reflect light. Putting a layer of a material whose refractive index changes over time between the glass and the air can make the transition of light from air to glass or from glass to air smoother, which reduces reflection.
The answer was found in nature: a fly's eyes have very small (nanometer-scale) bumps that are both convex and concave. This structure creates a layer with a very low refractive index, which stops light from reflecting. Canon technicians studied this idea in great depth and did a lot of trial-and-error experiments until they finally came up with a revolutionary coating technology that puts a layer on the lens surface with structure on the nanometer level. This is made up of bumps on the lens's surface that are only 200–400nm wide, which is smaller than the wavelengths of light that our eyes can see, which are around 400–700nm. The layer is spread out evenly on the lens's surface, leaving the edges open to air flow. This causes the refractive index to change gradually from the coating's tip to its base. This effectively absorbs light that hits the coating and guides it through the lens surface. The EF24mm f/1.4L II USM lens was the first to use this cutting-edge technology, which pushed the limits of what a wide-angle lens could do.