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I see the word "Coating" in different questions (related to lenses and filters). What are Coating, Multi-Coating, and Nano-Coating?

  • Nanocoating in specific is covered here. – mattdm May 14 '12 at 23:11
  • Also, tangentially (but importantly) related: What causes lens flare? – mattdm May 14 '12 at 23:13
  • The 1/4-wavelength trap described in jrista's answer in mattdm's first link is a fairly complete (almost exhaustive, really) explanation of coating/multicoating (short of a complete explanation of superposition, which is really out of scope here). – user2719 May 15 '12 at 1:36
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Coatings are just special chemical compounds that are applied to the surface of glass filters and lens elements in order to change their optical properties usually in order to reduce reflections and other unwanted effects, as well as repealing water and grease, and providing resistance to scratches.

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    what about multi-coating? what does multi mean here? – K'' May 14 '12 at 23:38
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    Multi is just more coatings, one over the other, with different material (different refractive index). Multiple layers allow for better cancellation of reflections more uniformly over the spectrum. – Skaperen May 15 '12 at 5:22
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This article from Roger Cicala gives a good overview:

Coating

Each interface between lens elements reflects light. It's not much, but because modern lenses are made up of many elements, the light that reaches the camera can be reduced dramatically.

A coating on a lens element reduces the amount of reflected light. That means more light reaches the camera.

Multi-Coating

Light is made up of different wavelengths. Think rainbow. A coating can only work for a specific wavelength. To block a range of wavelengths multiple coatings are applied.

Nano-Coating

A coating that has physical features small enough that light is not reflected at all. (very basically speaking) This is because light of a certain wavelength can only "see" objects of certain sizes.

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