The History and Science of Lenses


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 a bit of a mystery – perhaps it
was just 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’ play “The Clouds” from 424 BC mentioning
a burning-glass – a fire starting magnifying glass made out
of water filled glass sphere. In fact our word “lens” comes 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 eyes…But 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 prize… mainly
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 new “Schott” glass 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 it… the 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 off… and that was reflection – Double Gauss needed at least four elements
to work, most modern designs have up to 8 elements to control
aberration. Reflection, like the reflections we saw on the zoom lens laser demo, cuts down
on the amount of light that travels through the glass
– reducing its performance. The solution would come in anti reflective
coating. Back in 1896 Dennis Taylor working at Cooke noticed something peculiar about
older lenses – glass that had been sitting around for a long time
took brighter images. This was due to an oxidation layer that had built up through time that
suppressed reflection due to dispersion. By 1939, an
artificial coating was developed at Zeiss to cut down reflections as much as 66%. With
this improvement, the Double Gauss lens began to surpass the Sonnar
in terms of popularity. Hundreds of variations have been produced and millions of these types
of lenses sold. The common “nifty fifty” Canon and
Nikon 50mm lense are based on the double Gauss design. Now up to this time we’ve been talking about
strictly prime lenses – lens with only one focal length. The Variable focal length lenses
– a zoom lens was first patented in 1902 by Clile C. Allen.
Called Travelling, Vario or Varo lens, they didn’t see production for motion picture
camera until the late 20s, the first use of a zoom shot was
this one from 1927’s “It” starring Clara Bow. Motion picture film required less resolving
power than stills film. An acceptably sharp zoom lens for still photography didn’t come
around until 1959 with the Voigtländer Zoomar, 36–82 mm So with all these lenses being designed and
experimented with in the first half of the 20th century, an interesting shift occurred
at the close of World War II. So far we’ve been talking
about European lens manufacturers starting with the French, English and finally German
lenses which include the powerhouse brand Zeiss. But in 1954, as
part of the post war economic recovery campaign, Japan began to seriously push quality lens
production with manufacturing organizations Japan Machine
Design Center (JMDC) and Japan Camera Inspection Institute (JCII) banning the practice of copying
of foreign designs and the export of low quality
photographic equipment. They enforced it with a rigorous testing program that had to be
passed before companies could ship orders. By the 1960s
through a major industry push by the government, Japan’s lens industry began eclipse that
of Germany in terms of quality – with many German brands
closing up shop and licensing their name to products to be manufactured in South East
Asia. That also marks the end of naming lenses like Sonnar or Tessar
as the Japanese much prefered using brand names and feature codes to label their lenses.
The quality control organizations ended in 1989 having
completed their function but as a result when we talk about camera technology and lenses
today we almost exclusively speak about Japanese companies. I feel like we’ve only gotten a taste of
the world of lenses. In the next video on lenses we will focus on the properties of
modern day lenses – the basics of what you are looking when you put
a lens on to a camera. There’s been a lot of history and lot of science to get us to
today – so go out there, use it and make something great. I’m
John Hess and I’ll see you on FilmmakerIQ.com

Comments 100

  • as always, never fails to amuse me. can you guys make a topic about the story of distributing companies especially universal and paramount.

  • Thank you John Hess! For all you videos. You're an amazing teacher.

  • Thanks for this free class. You are the best!

  • I seriously love this channel.

  • another great video, keep going!

  • Cant wait for the next one.

  • Anamorphic lenses? :3

  • This channel is simply awesome! As a photographer, physicist and amateur filmmaker I just love every video. I want more!!

  • John, I loved your videos a lot. Can I buy these videos?

  • Awesome video! Love the explanation and use of the laser beams!! Can you explain one additional concept??!! One that has bugged me for a long time and have yet to understand: How does the aperture not affect field of view? I understand that it doesn't, but why? I am imagining creating a circle with my pointer finger and thumb and placing it in front of my eye. As I make the circle smaller, my field of view changes. In your lightbulb example at 13:53, I'm guessing if the aperture diaphragm was moved between the subject and the first lens, the field of view would change? I'd love to see the light beams passing through the aperture diaphragm. It would be very awesome to hear more about the placement of the aperture diaphragm in the lens sequence and WHY it is placed where. Meaning, if you had a 4 glass lens with the aperture diaphragm in the middle, WHY is it in the middle and what would happen if you took the aperture diaphragm and placed between the third and fourth lens instead. Thanks

  • Wow. Now that's a real optical demonstration; as good as MIT; and a lot cheaper !

  • This is awesome. Thanks

  • Great movie that i Will share a lot!

  • great video, but i fell asleep

  • You guys have so e great technical(non-) explainations. I was really into my Random House encyclopedia when I was younger.

  • Excellent!

  • Petzval was hungarian!!!!Please correct the video.

  • excellent! thank you

  • Who would've guessed that the best explanation of the physics behind lenses I would find would be produced by someone focused on cinematography.
    I watched at least 20 other physics videos about lenses and all those mooks like using rulers and markers to do their ray diagrams. Finally someone who uses some real life examples! Thank you

  • Great. Thanks. 🙂

  • fantastic once again!

  • Great stuff!

  • Ngl, this channel should be a series on tv

  • Absolutely fascinating. Loved it. Let's have more stuff like this please.

  • Very good lecture, I just have a Nikon D40, it's good enough for now.

  • This is the greatest teaching video I have seen on the internet so far and I have seen. I learned a lot and I will now start binge-watching your tutorials.

  • Well, I know quality when I see it, and both this man's presentation skills and video craft are most certainly it.

  • thank you that is great!

  • Seriously, great work with these comprehensive and clear videos. Keep it up!

  • I got so much info out of this – and it was demonstrated in a way I could understand. really helpful!

  • I love your series. Amazing. This was a great description of the history of lenses. However, don't forget one of the most amazing lenses, and fastest, used in Kubrick's "Barry Lyndon", the Carl Zeiss Planar 50mm f/0.7. This allowed for STUNNING images using only candlight.

  • sir…! you and your experiments are so awesome

  • If only my photography teacher had access to this! but it would have had to come in 16 mm film as the best tech we had back then was VTR in B/W.

  • I'm glad you didn't skip the Islamic contribution to science and math, a white washed common mistake in today's history is to go to Greek and Romans and then jump straight to Europe Renaissances skipping all the progress and development in science and math Islamic civilization brought in the Middle Ages.

  • Fantastic demonstration! Thanks for your video. But I'm confused with the zoom lens, if you adjusted the zoom lens, it seems like it affected the focal length too. Does it means if the image is zoomed in or out, the image will become blur since its focal length changed? You also added an aperture in between to increase the DoF of the system so the focal length didn't change much even the image is zoomed in or out?

  • As a physicist and film/film history enthusiast, I greatly enjoy watching your videos. My favorites thus far have been this one, the history of film fakery, and the video on the stargate sequence in 2001 Space Odyssey. Keep up the fantastic work!

  • Good videos, u have my sub!

  • John are an engineer or physicist ?
    What are you your main studies?

  • This channel is just great and awesome 🙂

  • They used an achromate for black-and-white dagerreotypes?

  • Could you share where you bought these supplies and what we would need to do this lab in class for our students?

  • your videos are awesome! thanks a lot

  • Man you are freaking good at this…these videos are the best I have ever seen on the subject.

  • wow. so educational 🙂

  • definitely should have more views

  • Does the color of light change due to it's slowing down in air? I guess it wouldn't matter because the length will go back to whatever it is inside our eye since no matter what medium the light passes through it's always passing through the same medium when it hits the cones and rods. If somehow someone got the fluid inside the eye changed he might notice a color change.

  • Great stuff. As usual. Clear and concise.
    But mathmamatics? 16:22 is that a real thing or did you stutter. 🙂
    (Il look it up now)

  • You guys are the best!

  • Wait at 6:28 when the light slowing down, why the refraction bending the laser down , not up, is it gravity can affect the light?

  • Fantastic video thank you so much

  • Mr. John Hess Thanks for your videos, I learn a lot from them.

  • I liked the way that you explained and showed us how zoom lenses worked.

  • Good stuff! Nicely done!

  • If my physics teacher was half as good as you were, I'd have enjoyed the class a whole lot more. Thank you Hess.

  • I want to actually correct you when you use the term 'slower' or 'slows down' when talking about refracting light. Light always travels at the same speed, regardless of the medium. We use the vacuum just for testing, when light passes through something it doesn't get slowed down, it takes an indirect(longer way) to reach the destination, therefore arriving later, but not because it was slowed down, but because it had more space to traverse. V=L/t. V is always 'c', don't ever say it's changing. You can change the L or the t as much as you want as long as divided they result 'c'. So yes, if you take the index of refraction and place that in the equation, you get the same thing, it's just the wording that was bothering me 'slows down the speed of light'

  • But did ibn alhaytham invent pure glass lens?……if not how did it reach him?

  • Anyone realized the speaker John Hess looks just like Josef Petzal's portrait at 16:23 ?

  • Such an entertaining & informative video that reflects the research & time spent on composition that was needed to create it !!! Well done !!! It's clarity & continuity are the result of a lot of work !!! I wish so much more had been presented in this way throughout my education – the best comment I can make is that " through this presentation – I undertook more investigation & research of the subject !!! Thank you

  • Thanks so much for this. Excellent video.

  • This was very, very interesting, thank you for making this video. Just a quick little note, the name was Charles Chevalier, not "Chavalier" (an "e", not an "a").

  • ok, mind blown, I dig the laser demos. 17 years as a photog and still learning.

  • excellent video

  • So basically, if it wasn't for a middle eastern immigrant, we wouldn't have cameras. Yeah, immigration is bad for the economy.

  • 25:27 minutes without pausing the camera! And every single word worths to be there… Thank heaven I found this youtube chanel, thank you very, very much!

  • This is more physics than theatre, but it´s ok

  • Wow man what a fantastic way to explain lenses and history

  • exotic learning.,,.,

  • I have a video pro class pretty fun

  • Great video and great teaching technique! You keep the video interesting all the way. Keep it up!

  • Informative but… Damn that Chalkboard noise !
    Completed now..Thanks A Tonne Mr.John..

  • Great video

  • As an electrical engineer i have to say your videos are very very very useful and love to watch.

  • Many thanks for this video, lots of useful informations.However, I found one contradictions with my own research. You mention Ibn Al-Haitham have produced pure glass lenses, but my finding shows the inventor of the process to produce pure glass through a process of converting sand into glass is Abbas ibn Firnas. Please correct me if I am wrong.

  • wow!!!

  • At 1:15, he says that the first mention that the first mention of a lens was by the Greeks, but this is way off. The first mention of a lens was around 2200 B.C. by Elihu in the Book of Job, chapter 37 (he calls it a "molten looking glass"). Everyone wants to leave out the Bible, but in the Bible is all "first mentions" of nearly every major item in existence. Why? Because if the Bible predates everything and is right, then it's right about what else is written in it. Read the Bible, the King James Bible (KJB), and learn where everything really began, and where you came from and who you are accountable to. Find the truth and hold to it. At 2:00 he gives credit to Muslims for many inventions, but King Solomon mentions all these things in the books of Proverbs, Eccl., etc. Again, the Bible predates them all. If you take note and watch, in the future, many, many teachers, etc. will only go as far back at the Greeks concerning most things that affect us today, but this again is false, the Bible, the KJB, predates anything they refer to as to the times of the Greeks. Why? Because, there are many that hate the truth and will do anything to remove the truth from you. But there is a God in heaven that has preserved it, in the KJB, so God has kept the truth available for you, that's because He loves you as His creation and will everything possible for you to have the truth of all matters, for the KJB says the "Spirit of truth will lead you into all truth." Not partial truths, or half truths, or 95% truth, but 100% truth. Yeah, that's how much God loves you and me. At 2:32 he again gives credit to the Muslims for the "Camera Obscura", but again, the Bible has this in it over 1,000 yrs early. The Muslim bible is packed with Bible passages and verses. They plagiarized the Bible and they have been changing "history" in America for the past 100 yrs.

  • I have become a huge fan of your teaching methods over the last 48 hours. I am a aspiring filmmaker and you manage to hit all points of interest. Thank you!

  • This is great. Thanks for putting it together!

  • Hey bro thanks for your videos. By far you are very informative and have a very pleasant delivery. Just started watching your videos and you could do a video explaining the science of tacos and I would watch it. Lol Cheers man!!

  • A key aspect of why lenses can project images is that at the image spot light comes almost only from the projection. Not the image surrounding, not the subject, not even the out-of-focus parts.
    This is why the "camera obscura" needs (and is named after) a dark room, but not a lens (a pinhole suffice).
    This is why your demo needs a bright subject (light bulb), since is has no dark room.

  • Wow! Your a "Super Cool Geek" ..
    ♡♡♡
    Because of you OPTICS is my new vibe!
    Where did u hide in my science years?

  • I feel like an excited child in science class!

  • So, if i get this straight; the Zeiss Touit Lens for Sony and Fuji is a double Gauss Design right?
    https://www.zeiss.com/camera-lenses/int/photography/products/touit-lenses/touit-1832.html#data

  • Watching this video is like striking gold. I normally watch Youtube videos at 2x speed or faster these days. I'm going to have to come back to this one when I have time to digest it properly.

  • terrifyingly good. I thought I knew about lenses :-O

  • John P. Hess, YouTube was a blessing for you, and you are a bless for YouTube.

  • Excellent

  • I'm rewatching your renewed video and as always you go deep and clear. But now I wish I would say something last time (in case you listen and change it) but when I explain the upside down picture I usually take a lens in a room where you could see the outside as shown from a window appear upside down. Maybe instead of a simple 2 color light bulb you could use (not sure I use the right word) a slide, like in a slide show where a colorful image will appear upside down and then it will be easier to see the focus effect

  • 6:20 when light leaves the aquarium it resumes its previous angle. But why? how does it regain its previously lost momentum? With air having a lower refraction index it means it is now traveling at a higher speed so how does it speed back up? I mean it's obvious that it can't, because that would break commonly understood laws of motion, gaining something from nothing, yet there it is.
    Have any insight into this, John?

  • You are the BEST teacher!

  • John, are you an optical physicist by training? Do you have duel degrees in both optical physics and film making?

  • First of all: great video!
    But I still have a question. When you buy a lens they always say how many individual lenses are used i said lens. What does this exactly mean? And is it better to have more or less?

  • This is the coolest demonstration I've seen on YouTube. If you did science videos, you'd probably be best science channel. I love the clear and easy to understand speaking style, the quality demonstrations, and the extra depth of research. I also like how you leave little mistakes in, which adds humanity. The thumbnails are also excellent branding. As soon as I see one, I instantly recognize it as an F-IQ video.

  • Waoo you’re really good

  • Excellent video, thank you for always putting out great quality content!

  • Best explanation of how a lens work I ever saw.

  • Cute opening credits, good Foley.

  • Really informative video, thank you

  • 01:57 this guy is still on Iraqi currency:
    https://www.amazon.com/ALHAZEN-GLOSSY-POSTER-PICTURE-currency/dp/B00AF1Q7GU

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