Lens Coating
Microscopically thin layers deposited on glass surfaces to reduce reflection and increase light transmission.
Formula / rule
Optimal thickness = λ / 4n
Measured in
nm
In depth
An uncoated air-glass surface reflects about four per cent of the light; with twenty surfaces that is most of the image lost to scatter. A quarter-wavelength coating causes reflections from its two faces to cancel by interference. Multi-coating stacks layers tuned to different wavelengths, raising transmission above 99 per cent per surface and dramatically improving contrast.
Examples in practice
An uncoated 1930s lens shoots milky and low in contrast against the light; a multi-coated modern equivalent holds deep blacks.