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Rayleigh (Resolution) Barrier Broken!


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Well, they’ve done it.  While you were sleeping and unbeknownst to most (but knownst to me), they’ve finally broken the “resolution barrier” – aka “The Rayleigh Limit.” That’s GREAT, you say.  But what is the “resolution barrier?”  Read on, my friends, and I will enlighten you…

First off, the “Rayleigh Limit” was named after its discoverer (as most things are) Lord Rayleigh, otherwise known as John William Strutt, the third baron Rayleigh – one of the few nobles to ever be recognized as a scientist.  In fact, he not only won the Nobel Prize in 1904 “for his investigations of the densities of the most important gases and for his discovery of argon in connection with these studies.”  Although his title granted him membership in the House of Lords, he rarely participated, and always put science before politics.

Still not ringing a bell?  Well, let me explain it another way.  Anyone who’s been to an eye doctor (or seen a doctor’s office depicted in an old movie or television show) has seen the familiar “Snellen Chart” for testing acuity of the eyes.  Created by Dr. Hermann Snellen, a Dutch Ophthalmologist in 1862, the chart hangs unobtrusively on the wall, usually in the background.  There is a giant letter “E” on the first line, and pyramid stack of letters underneath. In a typical eye examination, the doctor would have you cover one eye and then have you attempt to read the chart, from top to bottom, while standing at a distance of six (6) meters or about twenty (20) feet.

“Optical systems such as telescopes or cameras have been limited by a phenomenon scientist call the Rayleigh criterion,” explains UPI’s Ryan Maass, “which refers to the effects light has on attempts to resolve a point in an image. Due to the wave nature of light, points are blurred due to diffraction, effectively limiting the resolution.  Prior to the study,” Maass continues, “Rayleigh’s curse limited the minimum distance that can be distinguished with visible light.”

The recommended minimum illumination for Snellen charts is 480 lux.  “Lux,” you say?  What exactly is a lux? A measurement of 1 lux is equal to the illumination of a surface one meter away from a single candle.  Another way to look at 480 lux is three (3) 100-Watt bulbs in a 10’ x 10’ (or 100 square foot) room.  A bright office, for example, requires about 480 lux of illumination – or two (2) 75-Watt fluorescent bulbs in a 10’ x 20’ room (which allows for the distance needed to view the Snellen eye chart).  There are several formulas and calculations required to come up with the correct amount of watts needed to reach the roughly 500 lux for illumination, but I think you get the idea.

The Rayleigh Limit comes into play when trying to read the chart and reaching the first line that appears fuzzy.  Snellen calculated this fuzziness due to the resolution achieved based on the Rayleigh Limit and the ability to differentiate properly the letters on the eighth (8th) line of the chart (the line appearing just above the Green Line as printed on most charts).  This magic line is associated with the standard “20/20” vision, considered to be normal for most people.  The line can be easily read by a person standing 20 feet from the chart.  20/20 is about 12x the Rayleigh criterion.

According to the publication Optica (Vol. 3, No. 10 / October 2016 / pg 1144), “The Rayleigh criterion specifies the minimum separation between two incoherent point sources that may be resolved into distinct objects.”  This is illustrated by the picture below:

Rayleigh Limit

[Another example: Rayleigh scattering of sunlight in the atmosphere causes diffuse sky radiation, which is the reason for the blue color of the sky and the yellow tone of the sun itself.]

Let’s put this another way. When looking at the photo (above), you see photos a, b, & c; when you’re looking at one source of light, it’s easy to determine the edges of that singular source (like the glow around the outside of the moon at night, or its “halo”).  When there are two independent sources of light, even though the sources may be at two different lengths of distance from each other, the human eye causes the halos to come together, and a person can no longer discern where one source begins and ends.  The halo seemingly becomes one (as shown in photo c).

“In the recent experiment led by Complutense University physicists in Spain,” explains Maass, “investigators observed images with resolutions up to 17 times lower than previously thought possible.”  Thus, the Rayleigh Limit is broken.

This opens-up entirely new frontiers in optics, and will fold over into the media industry, as all high-resolution cameras (still or video) are hindered by this effect.  Personally, I can hardly wait to see the improvements coming in 4K, 8K and 3D display!

References:

“Lord Rayleigh – Biographical”. Nobelprize.org. Nobel Media AB 2014. Web. 8 Feb 2017. www.nobelprize.org/nobel_prizes/physics/laureates/1904/strutt-bio.html

Source: Boundless. “The Rayleigh Criterion.” Boundless Physics Boundless, 26 May. 2016. Retrieved 08 Feb. 2017 from www.boundless.com/physics/textbooks/boundless-physics-textbook/wave-optics-26/diffraction-175/the-rayleigh-criterion-640-6036/

“The Nobel Prize in Physics 1904”. Nobelprize.org. Nobel Media AB 2014. Web. 13 Feb 2017. www.nobelprize.org/nobel_prizes/physics/laureates/1904/index.html


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Ryan Salazar

Editor-In-Chief, Publisher at Broadcast Beat Magazine, LLC.
Ryan started working in the broadcast and post production industry at the young age of twelve! He has produced television programs, built large post production facilities, written for some of the industry's leading publications and was an audio engineer for about ten years. Ryan previously wrote for Broadcast Engineering Magazine, Creative COW and his projects have been featured in dozens of publications.
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