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  • Hi! John Hess from Filmmaker IQ.com and today we'll dive into the history and science

  • of lenses and how these little pieces of glass make filmmaking possible.

  • People have been fascinated by the properties of translucent crystals and glass since antiquity

  • long before we understood any about light.

  • The first lens or oldest artifact that resembled a lens is the Nimrud lens - dating back 750

  • to 710 BC Assyria. The intended use of this piece of

  • polished crystal is still a bit of a mystery - perhaps it was just used a decorative stone, perhaps it was

  • used as a magnifying glass for making intricate engraving or

  • perhaps it was used as a fire starter.

  • The Ancient Greeks and Romans give us the first recorded mention of a lens in Aristophanes'

  • playThe Cloudsfrom 424 BC mentioning a burning-glass -

  • a fire starting magnifying glass made out of water filled glass sphere. In fact our

  • wordlenscomes from the Latin for Lentil which is shaped like a

  • double convex lens.

  • But these first lenses were either polished crystals or water filled glass vessels - the

  • idea of producing a lens purely out of glass didn't come

  • about until the middle ages.

  • It began with this man: Abu Ali Hasan Ibn Al-Haitham, also known as Alhazen. Born in

  • Basrah in 945AD in what is now present day Iraq, he settled in

  • Spain where his ideas would found the basics of the scientific revolution including theories

  • on vision, optics, physics, astronomy and mathematics. He

  • was the first to accurately describe the eye as a receiver of light rather an emitter of

  • rays that the Greek scholars Ptolemy and Euclid believed. He

  • was the first to describe the camera obscura - a pinhole camera that had been known to

  • the Chinese but never written down.

  • But for our story today, Alhazen was key for his theories on glass lenses. Based on his

  • works, European monks began to fashion reading stones,

  • hemispherical pieces of polished glass that could be placed on top manuscripts to make

  • them easier to read.

  • This, as you could imagine, was a godsend for monks with aging eyesBut why stop there? As glass making became

  • more sophisticated, Italian glassmakers began making reading

  • stones thinner and even light enough to wear. The first spectacles appeared in Venice between

  • 1268 and 1300 AD. This mid-14th-century frescos by

  • Tommaso da Modena, featured monks donning the trendiest and most sophisticated wearable

  • technology of the time.

  • But Lenses weren't just for utility and fashion - they were about to be used for important

  • scientific study - that is being able to see things really

  • far away and really close up. The first refracting telescopes for astronomy were built by Dutch

  • spectacle makers in 1608 and refined by Galileo in

  • 1609. A few years later Galileo would alter a few elements on the telescope and create

  • the world's first microscope.

  • From opening up the vast cosmos, with Galileo observing the moons of Jupiter to inner space

  • revealing to Robert Hooke the microscopic cells furthering

  • our understanding of biology - the lens has been both a literal and metaphorical fire

  • starter for humanity's scientific understanding.

  • This is a good time in our story to stop and look at the science of how lenses work. It's

  • always a little tricky when looking at the history of

  • science because a lot of the basic understandings we take for granted today were total mysteries

  • to scientists back then..

  • Having said that though, let's cheat and apply some 20th century understanding to the

  • discoveries being made by people like Willebrord Snellius,

  • Christiaan Huygens, and Isaac Newton.

  • Let's start with a 20th century understanding of light. We now know that Light is a form

  • of electromagnetic radiation which also includes radio,

  • microwaves, infrared, ultraviolet, X-rays and gamma waves.

  • All electromagnetic radiation travels at the speed of light in a vacuum - a constant 299,792,458

  • meters per second (approximately 186,282 miles per

  • second). That's regardless of who the observer is.

  • But that is the speed of light in a vacuum.

  • When light travels through a medium, the electrons inside the medium disrupt the path light ray

  • - slowing it down. The amount of slowing down is

  • described by the material's “index of refraction” - the larger the index of refraction

  • - the slower light travels through that medium.

  • Air has a miniscule index of refraction: 1.000293 - so for anything that's not on a planetary

  • scale, it's negligible. Water has an index of 1.33. If

  • we shine a laser through an aquarium at an angle, we can see how the slowing down of

  • light bends the light beam as it travels through the water, once

  • it reaches the end of of the aquarium, the light beam continues along it's original angle.

  • But if we curve the surfaces of the entrance and exit points we can bend the light and

  • direct light beams along a different path.

  • To demonstrate I've created a few homemade lenses using gel wax. Using a square piece

  • of gel wax and a protractor we can determine the index of

  • refraction using Snell's law.

  • Now if we curve the surface - into a convex shape - here a double convex lens - we can

  • redirect a light beam. Convex lens will bend light inwards

  • where as a concave lens - here a double concave lens, will diverge light.

  • There's only so much you can do with homemade lenses. To explore the properties of lenses

  • we stepped up our experiments with real glass lenses and a

  • visit to YouTube Space in Los Angeles.

  • The first and most important part of a single lens is the focal length. The focal length

  • is the distance from the lens to the point where collimated

  • light rays, that's parallel light rays, converge. You can think of collimated light

  • as light coming from a very far away point in space - like the

  • sun. Using a pair of laser pointers and some fog, we can see that this convex lens has

  • a focal length of 130mm.

  • For determining the focal length of a concave lens - we would continue our diverging lines

  • backwards - this double concave lens has a focal length of about 170mm

  • So now let's talk about how we get a real focused image using a single lens. When the

  • object we're trying to focus on is very far away - we're dealing

  • with collimated light rays. So in order to get a focused image, we would need to our

  • imaging sensor at the focal length.

  • But not all light rays are collimated - light radiates from objects in a spherical fashion

  • and closer you are to something the more divergent the

  • light rays. So how does a lens focus the light from an object that's close? To solve this

  • question we have the thin lens equation 1/Distance from the

  • Object + 1/Distance to the image plane = 1/focal length.

  • First off let's talk about a really far away object. As the Distance to the Object

  • approaches infinity, the 1/distance to object approaches zero -

  • leaving us a little algebra and the distance to the image plane equals the focal length.

  • So far so good - but let's try to focus on something closer. Don't worry, we won't

  • get too crazy with the math - in fact it's easier to visualize with

  • a lenses and a couple of laser pointers and do some lens ray tracing.

  • We'll fire our first laser perpendicular to the lens. Once it hits the lens, it will

  • bend toward the focal point on the far side of the lens Now we'll

  • fire our second laser - this time aiming toward the focal point in front of the lens, so that

  • when it hits the lens it will be bent and exit in lens

  • at perpendicular angle. Where the lasers first meet in front of the lens is at our object

  • distance and where the lasers converge behind the lens is

  • where the focused image will be.

  • So in this first example, our object distance is 260mm and our focused image will be also

  • at 260mm using this 130mm lens. Notice how both distances

  • are exactly 2 times the focal length - and the math checks out.

  • Let's try another example this time with the object distance at 340mm. Using the same

  • 130mm lens the focused image will be at 210mm.

  • Notice how the beams converge beneath their origins, this means the image created will

  • be upside down. Laser ray tracing can be a bit abstract - let's

  • try it with a light bulb as our object and a piece of paper as our image sensor. Putting

  • the lightbulb at 340mm in front of the lens and paper at 210

  • does indeed yield a real focused image. Notice how shape of the light bulb filament is upside

  • down in the projected image and if we move our imaging

  • plane closer or further away we'll see the image go in and out of focus.

  • Now this works for a single thin lens with an object distance of over say about 2 times

  • the focal length. As the object distance gets closer to 1

  • times the focal length - the imaging distance approaches infinity - sort of the reverse

  • of what happened when we talked about collimated light. But

  • what happens when the object is inside the focal length?

  • Well the answer is we'll have a negative image distance. It's hard to simulate with

  • my experiment design but what you'll notice is the light never

  • comes to a focus past the lens - instead it looks like it's even more divergent. Let's

  • use a diagram to make it easier to see - again one ray

  • perpendicular to lens which bends to the focal point on the far side of the lens - and the

  • second ray coming from the focal point through the lens to

  • create a perpendicular ray.

  • The key here is our eyes and brain don't know that light is being bent by the lens

  • - we assume that all light rays are straight and continuous. So if

  • we follow the light rays back from the lens we end up constructing a virtual image behind

  • the object - right side up and magnified- this is how a

  • magnifying glass works.

  • The real fun occurs when we bring more than one lens into the mix. Telescopes use an objective

  • lens with a long focal length and an eyepiece lens for

  • focusing - the lenses have to be placed inside their focal lengths in order to work. A microscope

  • switches out the objective lens with its long focal

  • length for a lens with a very short focal length.

  • Combining multiple lenses also allows us to change the magnification - here is a model

  • of an afocal zoom lens - using two convex lenses with a concave

  • lens in between. As we move the concave lens we change the distance of the beams entering

  • the lens system. Focus on the bright green beams, the others

  • are reflections created by inferior glass. Notice how the beams change distance as I

  • move the middle double concave lens. Using a light bulb in place

  • of the lasers and an aperture on the final focusing lens to increase the sharpness, we

  • can see this zoom lens in action.

  • The demand for better and better lens systems for scientific discovery kept lensmakers busy

  • throughout the 17th and 18th century, but the coming age

  • of photography would bring a whole new game to town.

  • THE INFANCY OF PHOTOGRAPHY

  • The very first lenses used for photography in the 19th century were single element pieces

  • of glass just like in our science demonstration. But the

  • problem is, there's a lot of photographic issues from using just one lens including

  • Chromatic Aberration - that's where light of different

  • wavelengths get bent differently as they pass through a lens. Anyone who wears glasses can

  • see this effect when they look at a neon sign that has blue

  • and red lights, Spherical Aberration - where not all light rays are converging at the focal

  • point, and Coma Aberration - where off axis light smears

  • creating a comet like tail. These are just a few of the problems image makers have to deal with.

  • The first widespread photography process - the French originated Daguerreotype used a lens

  • by French lensmaker Charles Chevalier in 1839. This lens

  • was an achromatic doublet, cementing a biconvex element of crown glass with a biconcave element

  • of flint glass. These two types of glass have

  • different properties and combined these lens greatly reduced chromatic aberration leading

  • to sharper images. This early lens used an aperture, a small

  • hole that reduces the angle of the light rays coming in which further increases sharpness

  • but reduces the amount of light available for the film. With

  • an aperture of f16 - f stop is the ratio of the the lens' focal length to the diameter

  • of the aperture, this lens was very slow - taking twenty to

  • thirty minutes for an outdoor daguerreotype exposure. Because of this limitation, this

  • lens became known as the French Landscape Lens.

  • For portraits, especially indoor portraits, a new type of lens configuration was needed.

  • In 1840 the French Society for the Encouragement of National

  • Industry offered an international prize for just such a thing. Joseph Petzval a Slovakia

  • mathematics professor with no background in optics with the

  • help of several human computers from the Austro-Hungarian army took up the challenge and submitted his

  • design in 1840 - the Petzval Portrait lens.

  • This was a four element lens which had an aperture of f3.6 - much faster than the Landscape

  • lens - a shaded outdoor sitting would only take a minute

  • or two and with the new wet collodion process for photography and this lens could even expose

  • an indoor portrait in about a minute.

  • But Petzval didn't win the prizemainly because he wasn't French, but his lens would

  • go on to be a dominant design for nearly a century - it was

  • sharp in the middle but fell out of focus quickly on the sides which gave those portraits

  • from the 1800s that soft edge halo focusing effect.

  • And although Petzval lens was a mathematically devised lens, lensmaking would resort to trial

  • and error for the next 50 years which included the first

  • wide angle Harrison & Schnitzer Globe lens of 1862 and the Dallmeyer Rapid-Rectilinear

  • (UK) and Steinheil Aplanat from 1866.

  • These four lenses, The French Landscape, the Petzval Portrait, the Globe and the Rapid-Rectilinear/Aplanat

  • were the four go-to lenses of the found in

  • the 19th century photographer's bag.

  • Heading into the 20th century, the story of lenses simply explode - we'll take a look

  • at a few notable examples and historical.

  • Lens technology took at huge leap forward in 1890 with the release of the Zeiss Protar.

  • For the first time since the Petzval Portrait we have a lens

  • designed based on scientific formulas to reduce all lens aberrations including astigmatism.

  • Part of the key to success is the use of a new Barium

  • Oxide Crown glass developed by Carl Zeiss' Jena Glass Works by Ernst Abbe and Otto Schott.

  • This newSchottglass had a higher index of refraction

  • making it key the development of better optics.

  • Now with better materials the cat was out of the bag and new designs for lenses flooded

  • the marketplace.

  • In 1893, Dennis Taylor who was employed as chief engineer by T. Cooke & Sons of York

  • patented the Cooke Triplet as a result of the new designs made

  • possible by the invention of Schott Crown glass. The Triplet featured three elements,

  • the center element being flint glass while the other two being

  • crown glass. The Cooke Triplet came to dominate the low end industry - even used in modern

  • projector lenses, binoculars, as well as some of the early

  • motion picture lens of the 20th century.

  • But the folks at Zeiss weren't done just yet - Paul Rudolph working at Zeiss patented

  • the Tessar in 1902. Similar to the Cooke Triplet, it added a

  • fourth glass element greatly improving performance. The Tessar design is still used on a lot of

  • pancake style lenses.

  • As aberrations came under control with these new lens designs, attention turned to increasing

  • the aperture size to allow for faster shooting.

  • Ernemann Ernostar in 1923 opened up the aperture of a 85mm up to an f2.0 and later to f1.8

  • in 1924 leading to a new era of photo journalism as less

  • light was needed to expose a photograph.

  • In 1926 Ernemann was absorbed by Zeiss and the Ernostar design was reworked and renamed

  • Sonnar - by 1932, a 50mm f1.5 was available.

  • Another notable style of lens design was the Double Gauss lens. Named after the mathematician

  • Carl Friedrich Gauss. The double Gauss took what was

  • originally an objective lens for a telescope and doubled itthe resulting lens has become

  • the most intensely studied lens formula of the 20th

  • century. The Gauss design greatly reduced optical flaws in almost every way and these

  • lenses could be made with really wide apertures and relatively

  • inexpensively. Although the first commercially successful double gauss - the Taylor, Taylor

  • and Hobson Series 0 was released in 1920, there was a

  • problem that prevented the Double Gauss from really taking offand that was reflection

  • - Double Gauss needed at least four elements to work, most