Why all the different colors reflected from lenses within lens lines and from different manufacturers? My Zuiko lenses reflect brown tones, and my Leica lenses vary from blue to violet to brown to mixed.

It would seem, since our light source (sun) doesn't change that quickly, geologically speaking. I mean, the makers should make coatings that maximize light transmission and neutral color renditions. Coatings should not be related to the types of glass used in the lens (maybe yes, to cancel out lens effects?). Should ALL coatings look the same?

-- chris chen (chrischen@msn.com), March 12, 2002

Answers

Chris:

Old uncoated lenses reflect white lights as white as they reflect all colours.

Multi coated lenses show three basic coulours- Cyan Magenta and yellow-more or less- as they absord all colours and each coating reflects the colour it does not absorb. Monocoated lenses reflect a single colour becaues they allow some to pass and reflect others inside and outside the lens. All glass-air surfaces are coated thus decreasing the internal reflecting that cayse flare and ghosting, as well as decreased contrast due to reflected light getting into shadow areas where there should be none.

At least that is what I remember from the texts.

Cheers

-- RICHARD ILOMAKI (richardjx@hotmail.com), March 12, 2002.

Coatings work by cancelling reflected light using wavelength interference.

The coatings are roughly half the thickness of the light wavelength (which is different for each color). Light reflects off both the glass and the coating, but since the reflections are out-of-step by 1/2 wavelength, they cancel out and the light disappears.

Single coatings (c.1940 - 1972) cancel one wavelength of light - leaving the others visible. It's sort of up to the designer and chemists to decide which wavelength it's most desirable to cancel - or which coating is most cost-effective to apply - so the remaining light color varies from lens line to lens line.

Multicoatings have several layers - each a different thickness - and so cancel light of several colors (wavelengths) leaving just a small amount of reflected light - blue, violet, yellow, or the mix that looks brown. Again it varies with the production process and compounds chosen. But note that the color is related entirely to the THICKNESS of the coatings, not the coating chemicals themselves (which are transparent).

The purpose of coating is to maximize the elimination of reflected light from the glass - not to bias the color one way or the other - so the 'color' we see looking into (not through) the lens is just a by- product of the coatings chosen and the physics involved.

-- Andy Piper (apidens@denver.infi.net), March 12, 2002.