Lens Coatings

[chris_chen]

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.

 

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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?

[richard_ilomaki]

Chris:

 

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

colours.

 

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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.

 

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At least that is what I remember from the texts.

 

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Cheers

[andy_piper2]

Coatings work by cancelling reflected light using wavelength

interference.

 

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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.

 

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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.

 

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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).

 

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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.