Air Sphere Coating (ASC)
Air Sphere Coating (ASC) is a lens coating technology that was created to make photographic lenses less reflective. Canon invented Super Spectra Coating (SSC) to get rid of ghosting and flare and keep the colour balance even. They also came up with the revolutionary Subwavelength Structure Coating (SWC), which stops light from entering the lens at high angles of incidence and makes it much less reflective. If you use the new ASC technology with SWC, it makes lens flare and ghosting even less likely.
When secondary reflections happen between the lens elements and the image sensor, they distort light or cause other effects that lower the quality of the image. This is what causes ghosting and lens flare. When shooting into the sun or in other situations with a lot of backlight, lens flare, which looks like a white spot that is too bright, can cover up part of the image. Reflections on the lens's surface can also show up in the picture as extra stuff (ghosting). ASC is the latest step that Canon has taken to improve coating technology. As a result, lens flare and ghosting are much less likely to happen because light always hits the image sensor's surface at the right angle.
Adding a thin film of silicon dioxide and air on top of the vapour-deposition lens coating stops light from reflecting. This is called ASC technology. The coating has just the right amount of air in it, which has a much lower refractive index than optical glass. This gives the layer an ultra-low refractive index. It is very good at not reflecting light because of this, especially light that comes in at an angle almost perpendicular to the lens. When ASC is combined with SWC, which stops the secondary reflection of light coming in at high angles of incidence, any extra light entering the lens can be stopped, no matter what angle it comes in from, effectively stopping lens flare and ghosting. ASC doesn't put as many limits on lens design because it can be used on surfaces with different curves.
