Let's imagine simple old lenses like Planar, Sonar, Tessar. Tessar has 4 elements in 3 groups. It means 2 lenses are glued together (with canada balsam because its refractive index is same as glass). Consider these two glued lenses are one optical element. There is no coating between them. So to simplify it consider we have 3 elements only. Each of them has 2 surfaces. Let's name surfaces (from outside towards the chip) as A-B, C-D, E-F. A-B is the first glass/lens element, E-F is the last lens/element closest to chip. I don't consider any filter (but if you want, add filter as 1 additional element and just add 2 letters). I don't consider any diffraction nor absorbtion on glass and coating layer (lens elements are perfectly smooth and glass is clear).

Antireflectioncoatingprinciple PDF

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2.: AR coating on "A": there is approx. 2.2% reflected light from "A", transmission is 97.8%. (But these 2.2% of reflected light are eliminated during destructive interference because of opposite phases of waves reflected from glass and from coating-as explained above.)

There is no impact to picture quality what filter reflects outside of the lens. And, as I understand, the amount of light entering into lens is still the same. The amount of light (energy) reflected out of lens (or filter) is still the same too. Just the both outgoing waves are subtracted and are not visible for outside observer. How can anti-reflective coatings on outer lens surface influence inner light inside the lens?

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But 0.086% is about -10EV difference only (=log ( 0,086% / 100% ; 2) ). Such flares are barely visible... And where is 50% improvement of transmission?

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Since then, USB technology has advanced even further with USB 3.2 arriving in 2017. There are four different variations of USB 3.2 with their own special names and meanings. Four variations of USB 3.2 are:

USB 3.0 was released over ten years ago in 2008 and it was the third major revision to the USB standard. It was a big improvement from USB 2.0 which first arrived in 2000 with transfer speeds of only 480 Mbit/s. Since then, we’ve moved on from USB 3.0 which is now known as USB 3.1 Gen 1. Therefore, USB 3.0 is the same thing as USB 3.1 Gen 1.

This discovery and remedy are important as modern lenses often use many elements and groups. Losing 4 to 6% at each surface (glass to air junction). In a multi-element lens system, this translates to a very high loss, could be 50% or more. Plus, each internal reflection caused light rays to go astray, many misdirected rays will bath the film/chip with light scatter called flare. Flare is devastating; it degrades the image by reducing contrast. Gross reflections cause glare spots.

Anti reflective coatingsunglasses

Calculation is based on indexes n=1.5 (glass), n=1.3 (coating), total light falling to lens is 100%, formulas for refraction and reflection are below (see Steven Kersting - thank you). Coating is on the "A" surface only.

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But: why is anti-reflective coating on front lens surface and are not on inner lenses? Or why is anti reflective coating on filters??

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With the arrival of USB 3.2, the industry dominant USB-A connection was beginning to phase out in favor of USB-C. Since USB-C supports higher data transfer speeds and could charge other peripheral devices faster, it has naturally become the main USB connector in utilizing USB 3.2 Gen 2.  What does x2 mean?  If a device has this designation it uses 2 of the available data lanes.  Learn more about USB 3.2 Gen 2x2.

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Anti Reflective coatingPhysics

If there is no coating on "A", the calculation will be similar and result will be slightly worse (about 1,5% light will be reflected from inner surface of "A" back to "B"). Negligible difference..

Schlieren imaging is a surreal technique that leverages the principle of refraction and lets you visualize air density gradients (in short, it ...

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Any single coating that reduces losses (scatter/stray reflection/etc) is beneficial, and it is that first interface that is most critical... but most modern lenses/filters have all/most glass-air interfaces coated.

First, contrary your understanding, it does increase transmission. An uncoated glass surface reflects about 4% of the light that passes through it (entering or leaving the glass), which is much of why lenses with more than four elements were uncommon before the advent of coating technology. Multiply 4% loss over 6 glass surfaces even in an 1890s technology Cooke Triplet type lens, and you're already down to only 78% transmission (not even accounting for filtration losses inside the glass elements). A Tessar type adds a cemented interface, which loses less than 4%, but still has those six glass-air surfaces. The f/2 Xenon on my 1941 Weltini, with six elements in four groups, has no more than 72% transmission (probably a little less, since there are cemented interfaces as well). Obviously, this is all air/glass surfaces, but even reducing the first 4% loss is significant for low light applications.

An AR coating is not intended to decrease light transmission; in fact, it is the opposite. "Anti-reflection" can be equally considered to be "increased transmission/transparency". Incorporating a coating with a lower refractive index on a lens than the refractive index of the optic itself reduces the overall refractive index of the constructed element. In this example a single coating with an RI of 1.3 increases the light transmission to 0.978 (97.8%).

Antireflectioncoatingformula

I still remember when I calculated the thickness of layer (with given refraction index) to increased or decreased appropriate wavelength at school...

In the edit of the original question, we see this: "Just the both outgoing waves are subtracted and are not visible for outside observer." Sorry, you don't understand how destructive interference works. Light that's phase shifted a half wavelength isn't just invisible, it's forbidden by physics. That is to say, the light never reflects at all if doing so would produce a half-wave interference. This isn't what happens with coatings, however; if it were, there would be color fringes like in a soap bubble, as different viewing/reflecting angles interacted with the thickness of the coating. Instead, the coating makes the interface less "abrupt" to the incoming (or exiting) light, like finding a drop curb at a driveway instead of trying to climb the regular curb.

Taylor experimented and found a way to artificially bloom (age) lenses. This truly was an important discovery because new lenses suffer a 4 to 6% loss in light due to light being reflected from their polished (mirror like) surfaces. Now lenses used in cameras and telescopes are complex systems with many lens elements sandwiched together. Thus, multi-lens element systems can suffer a light loss of 40 – 50%.

The optical density of any material is directly related to the refractive index of that material. The more is the optical density, more will be the refractive ...

Alan Marcus wrote about light reflected from "B" surface backwards to "A" in comment below (thanks Alan). There is no coating on "B" so 4% of light are reflected from "B" backwards to "A". It is exactly 3.9% (=4% x 97.8%). Returned light is transmitted through "A" ( 3.81%=97.8% x 3.9%) and 0.086% (=2.2% x 3.9%) is reflected back from inner side of "A".

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Third, reducing reflection at the first surface limits the strength of light source image reflections from whatever filter(s) might be mounted in front of the lens (these are the dazzle spots you see in an image where a bright light source like the Sun is in or barely out of frame). These are the Michael Bay dazzle spots.

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The difference between USB 3.1 Gen 1 and USB 3.1 Gen 2 is only in terms of speed. USB 3.1 Gen 1 supports speeds of up to 5Gbit/s while USB 3.1 Gen 2 supports speeds of up to 10Gbit/s. The USB-IF intended to use a set of different names to call the USB 3.1 Gen 1 and USB 3.1 Gen 2 that would’ve made it better strictly for marketing purposes. They wanted to name USB 3.1 Gen 1 and Gen 2 "SuperSpeed USB" and "SuperSpeed USB+" respectively, but the industry never caught on. Often, OEMs will add the speeds of 5Gbps or 10Gbps to their spec tables in order to differentiate between the two USB standards. The rest of the industry just refers to them as "USB 3.1 Gen 1" or "USB 3.1 Gen 2."

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Anti reflective coatingdisadvantages

Many coating methods are used. One method is to place the lens to be coated in a vacuum chamber. The air is evacuated and the mineral that will be the coat is heated causing it to vaporize. This vapor condenses on the glass lens and coats and etches. It is the thickness of the coat plus the material that does the trick. Each coat is optimized for just one color of light. A modern lens has multiple coats applied. Each coat is different in thickness. A high-quality lens can have as many as 7 thru 11 coats.

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Second, coating reduces scatter at each air/glass interface -- scatter being light that is neither transmitted directly nor reflected. In general, the lower the reflectivity of a surfac, the less it scatters as well. Scatter produces "flare" -- which isn't what you see in a Transformers CG shot, but instead is an overall loss of contrast due to light from bright areas being scattered into what should be dark areas.

And I didn't consider different behavior of coating on "A" for inner light (light reflected backwards from "B" to "A"). Inner light enters from more dense to environments with less density so light wave has the same (not opposite) phase. There are no coatings on B, C, D...

The British Physicist (Nobel Prize) John William Strutt, 3rd Baron Rayleigh, in 1886 discovered that old lenses on the shelf passed more light than new ones of the same design. Carrying on, the English optician Harold Taylor, in 1892 figured out why. Seems old lenses were blemished with soot. This was during the industrial revolution and the air was laden with smoke and soot from the coal fires that powered the steam engines and gave warmth. This coating of atmospheric pollution settled on lenses on the shelf and etched them. He discovered that this thin transparent coat somehow reduced surface reflections allowing more light to transverse the lens.

USB came a long way from when it was first introduced and will continue to advance in the future. When it comes to USB 3.1 Gen 1 and Gen 2, the only difference is speed and they're backwards compatible with USB 3.0 and USB 2.0. In the future, with newer generations of USB standards and the arrival of USB-C, there will be even better improvements.

In this example I considered only the first lens element (A-B). There are much less light from the second and from the third element. Another -10EV difference.. There are other reflections, of course. From C to B and A, from D to C, B and A... I ignored them to simplify this text...

There is an inverse relationship between distance and light intensity - as the distance increases, light intensity decreases. This is because ...

USB-IF, the organization that is responsible for maintaining USB (Universal Serial Bus) specifications and compliance, did this to make it easier for developers and manufacturers to have the same relevant information to ensure products are properly developed to be backwards compatible. They are responsible for the naming conventions found on USB cables and devices.

Principle of anti-reflective coating is very simple: thin layer between air and glass returns light wave in opposite phase. Or to be more precise: anti-reflective layer shifts light wave about 1/2 of wavelength. So light waves reflected from surfaces 'air/coating' and 'coating/glass' are subtracted (destructive interference). The reason is to increase light transmission, decrease inner lens flares and increase contrast of lenses.

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