I am sure you have noticed the different colors of coatings on your lenses. And today, we are going to explain why the lens manufactures do this.
When you look at a lens, especially off to the side, you see beautiful colors of green, blue and even red. A thin coating is vacuum deposited onto the surface of the lens to reduce the amount of light that reflects off the lens surface or inside the lens, and to increase the amount of light passing through the lens. The surface of a coated lens appears to sparkle with a range of colors, including red, green and blue.
Camera lenses in particular have much more coatings on their lenses than eyeglasses. Good eyeglasses have coatings on them as well. But a camera lens has coatings on almost all of the different lenses within the lens barrel itself.
Are these coatings worth it? When I first got into photography, I actually thought that the colors and sharpness have been diminished because of the coatings, but, after selling the lenses myself, I found that it of utmost importance to have coatings on lenses. Without bothersome reflections, more light is able to pass through your lenses which optimizes your vision. Fewer distractions are visible (especially in the dark), and the lenses are hardly noticeable. Most people agree that anti-reflective coatings on their lenses are definitely worth the added cost.
The proper name for these coatings is actually: anti-reflective coatings. An antireflective or anti-reflection (AR) coating is a type of optical coating applied to the surface of lenses and other optical elements to reduce reflection. In typical imaging systems, this improves the efficiency since less light is lost due to reflection. And I remember reading about this years ago, and had no idea that these lenses had issues with light reflectivity. Now I know. And very grateful for these coatings.
Ordinary glass lenses transmit most of the light that hits them, but even so, about 4% of this light is lost to surface reflection. Since lenses have front and rear surfaces, this means that the overall loss of light from passing through one lens element is 8%. Most camera lenses are made up of five to 10 elements, and so in the end, the total amount of light getting through the lens is reduced by about 50%. Lens coatings were developed to prevent surface reflection and boost light transmission. Coating lenses enables more light to pass through them. I had no idea that there was that much light loss on each element of glass. Now I have high respect for these camera lens manufactures.
Coatings on lenses actually reduce the phenomenon called “ghosting”. Surface reflection reduces the amount of light transmitted through a lens, but this is not the only adverse effect. Reflection within the lens also causes such problems as image duplication, and the transmission of non-image light to the image: phenomena known as ghosts and flares, respectively. Ghosts are created when light reflected from the rear surface of a lens is reflected once again from the front surface, resulting in a faint second image slightly displaced from the primary image. Flares appear when light from the back of the lens barrel is reflected from the lens surface onto the image. Ghosts and flares caused by surface reflection reduce the quality of the image produced.
Surface reflection can be reduced by applying coatings to the lens surface. You might think that coating the lens surface would block light, but in fact it increases light transmission. This is because light is reflected first by the coating surface, and then by the lens surface itself. The light reflected by the coating surface and that reflected by the lens surface have a phase difference of twice the coating thickness.
If the thickness of the coating is one quarter of the wavelength of the light to be suppressed, light of that wavelength reflected by the coating surface and light reflected by the lens surface will cancel each other out. This reduces the overall amount of light reflected. In short, coatings make use of light wave interference phenomena to eliminate reflections.
Now to really get you excited, I have a special video presentation on how Nikon makes their lenses. Click on this link to see it: https://www.youtube.com/watch?v=s4BOLIa_3lw
This might be another good video: How to pick a lens, as told by Pentax: https://www.youtube.com/watch?v=GAUQ4SVpE98
And finally, why are lenses so expensive? https://www.youtube.com/watch?v=2eNDMRKtCNY