In this article, we look at anti-reflection lens coating, providing a guide to what it is for, and how it works
Camera lenses can be beautiful things to behold and almost gem-like. Much of this beauty is thanks to anti-reflection lens coatings which can appear as multi-coloured tints when viewing the glass in a lens. Older anti-reflection lens coatings often only exhibited an amber hue, or maybe amber and purple if a double coating was used. Yet being pretty is not their purpose, as they dramatically reduce the amount of internal reflections in a camera lens and make the lens more efficient.
Anti-reflection lens coatings also reduce flare and ghosting. Flare is characterised by bright circular artefacts that are the shape of the lens aperture iris, as well as hazy areas of unwanted brightness and reduced contrast, usually when the lens is pointed at a very intense source of light. Ghosting is where a secondary image is formed because of internal reflections, usually seen when the subject is extremely bright and high in contrast. The coating helps by enabling more of the light to be transmitted through the lens instead of being reflected.
The anti-reflection lens coating also tackles light that is reflected by cancelling much of it out. Under certain light you can see several hues, predominantly green, on the surface of the glass lens components that make up a camera lens. Uncoated lenses may lose as much as 5% of light transmission and modern camera lenses can contain more than a dozen lens elements, so it all adds up. Lens coatings can reduce losses to a fraction of a per cent.
A lens coating is an incredibly thin layer of optically clear material of a selected refractive index that suppresses reflections in the first place. However, if light is reflected the coating reflects the reflection in a phase that means the waveforms destructively interfere and much of the unwanted reflection magically disappears. Multiple layers of anti-reflection coating deal with more wavelengths or colours of unwanted reflections, playing a hugely important role in improving the efficiency and usability of lenses.