Lens Coatings 101

A camera lens is made up of many smaller lenses called elements. At each interface between air and glass, there is an opportunity for a reflection to form. The reflected light can bounce back and forth between the different elements in a similar way to having two mirrors facing each other. This results in lens flare and loss of contrast in the picture.

Since light has characteristics of a wave, the reflected light can be cancelled out by another wave in opposite phase – just like noise canceling headphones. The idea behind lens coating is to use the reflection from the coating to cancel out the reflection from the glass. So, for any given wavelength you can get perfect cancellation of reflection of glass by applying a wavelength divided by 4 thick layer of material that had a refractive index halfway between air and glass.

The problem is that light is not made up of one wavelength -- it is a continuous range from 400 to 700 nm. Moreover, both film and digital sensors have some sensitivity to infrared and UV light beyond that range. With a single antireflective coating targeting 550 nm, you'd get great anti-reflective properties for that wavelength but lose the effect the further your wavelength deviated from that central point.

This is where multiple anti-reflective coatings, or multi-coating, comes into play. It's the same idea of canceling out the reflection from the glass with the reflection from the coating, but each layer of coating targets a different wavelength. It's substantially more complex to decide which wavelengths to target, what material to use for each layer, and even how many layers to apply. The high-end lens manufacturers all have their own formulas and approaches which ultimately results in the Leica sparkle, Carl Zeiss glow, or Sigma yellow. Going from a simple multi-coating to a higher-end multi-coating can double the cost of each coated element in the lens.

All of the Leica lenses used in the Lumix line-up use identical multi-coating to that found in the M- and R-mount Leica lenses. In comparison, most of the Carl Zeiss lenses used in Sony digital products do not use the famed T* coating. Since the Panasonic Lumix cameras use Leica's multi-coating, it is in fact a real Leica lens.

Skeptics may point out that Leica lenses used in Lumix cameras are manufactured in Japan rather than Germany. The country of manufacture shouldn't affect what is real and what is not. No one reasonable would ever claim that the Carl Zeiss T* lenses from Contax, or the five lenses for the new Zeiss Ikon rangefinder manufactured by Cosina were somehow only a collaboration of marketing. Others will point out that the lenses in Lumix line don't have the same image quality as M- and R-mount Leica lenses. This is true.