Hello there, my name is Jake Roper
and, oh, you probably can't really see me
right now let's throw a lens on that camera.
Ah, there we go.
Look at that.
Let's just lock it into place.
ooh.
Much better.
Now look deeply into
my eyes, we’re seeing each other through
3 lenses, 4 if you wear glasses.
Now, light is coming off of my eye and going
through
my glasses and into the camera lens, and then
out of your screen into the lens in your eye.
In fact, let me grab one, most camera lenses
have many pieces
of glass stacked inside of them, so while
we call this single piece of equipment a lens,
there’s actually many different “lenses”
bending light between the two of us.
And we’re gonna take a look with our eyeball
lenses, at some optical DONGs, things you
can do online now guys.
Ricktu’s Ray Optics Simulator is a great
way to visualize how light moves around when
distorted by various surfaces.
You can make beams, rays and other light phenomena,
interact with various reflective and translucent
surfaces.
You can change a whole bunch of factors, like
the density of the beams and the shape of
the reflective or transparent surfaces.
So why does light bend like that?
We’ll get to that in a second, but first
let’s talk about why light can go through
things at all.
You can’t see through me, or at least I
hope you can't
So what makes glass so special??
When a photon hits something opaque, like
you or me, it either scatters away in a random
direction or it’s absorbed by the material.
Transparent materials on the other hand don’t
absorb light, but instead let it pass right
through, and that’s what a simple sheet
of glass does.
The science of why this happens is very cool
and very complicated, 60 symbols has a wonderful
video on the topic, you can check it out right
here
but basically when light hits an object, the
energy in the photon is absorbed by the electrons
in the object’s atoms.
With glass, however, the price of entry is
a bit too high, and the atoms in the glass
want more energy than visible light can provide,
so the light just keeps on truckin.
This applies to visible light, but not so
much for UV light.
Check out my video from last year where we
use predator vision.
It's all about UV cameras.
and ultraviolet and infrared.
Anyway it's really cool.
See this?
This is a lentil.
The word lentil is where the word Lens comes
from.
Lentils were never used to make lenses or
anything, but they look the same a basic lens
shape.
Legumes are a tasty treat.
Anyway, lenses, or really any curved glass,
bends the light that passes through it.
Jake!
How does this work??
Well my inquisitive little turtle:
Great Question
it takes advantage of two fundamental
properties of light.
The first is that light slows down in certain
types of materials, like air, water, and glass.
Now you might be saying “ i thought the
speed of light was constant” well that’s
just the speed of light in a vacuum.
Again, there’s a lot of weird quantum stuff
going on, but the important thing is that
once light enters other mediums, it’s forced
to interact with the other atoms hanging around,
and those interactions slow everything down.
The second property of light is that it is
not just a particle, but also a wave, which
means it fluctuates in three-dimensional space.
Imagine a group of runners all running next
to each other, tied together with ropes.
If the group starts running through mud at
an angle, one of them will be slowed down
faster, and the others will have to change
angles to stay parallel.
That’s essentially what’s happening when
light curves through a cup of water or a camera
lens.
This allows us to do all sorts of crazy things
to incoming light.
You probably have zoomed in to something with
a camera before.
If you have, you may have also seen these
levels of magnification measured in millimeters,
for example, this video is being shot on a
50mm lens.
That number measures the distance between
the front lens and the back lens.
This is called the focal length.
On this site you can get an idea of what focal
lengths look like in real life.
You can mess with the actual zoom of the camera
as well as the camera body that captures the
image.
Seems pretty straightforward right?
Well it’s actually a very complex process
to make sure that the image stays sharp and
consistent while changing magnification, and
it involves many layers of glass of different
shapes.
when you twist a zoom lens like this you’re
actually physically moving the piece of glass
around inside.
Some lenses actually stick out when you do
this.
What this does is move what’s known as an
“afocal zoom system,” which involves a
few concave lenses (lenses that bend light
inward) with a convex lens between them (which
bends light outward).
So as the light from the object you want to
magnify comes in it gets focused and then
re-spread out to make the image appear bigger
on the image sensor.
Keep in mind that there are some types of
lenses that don’t zoom, and they’re called
prime lenses, oh and if you zoom in on your
phone it’s not the same process.
that’s just the camera enlarging the digital
image rather than actually bending the light
to make an object appear closer.
It's the same thing we do in our videos where
we punch in to make it look like it's a closer
shot
when it's really like this
Ok, so you can zoom in all you want, but
going back to the beginning of this video,
what about when everything is out of focus??
Michael just did a DONG episode on how to
use a pinhole
to create a 2 dimensional image,
and a perfectlysmall pinhole will create a
perfectly sharp image.
As we make the opening bigger, we’re going
to end up with more blur.
On a camera lens the system that measures
the amount of blur is determined by the size
of the opening, also called the aperture or
f-stop.
This website lets you get an idea of how changing
the fstop changes the level of blur around
the object that’s in focus.
Now anyone who uses cameras regularly has
noticed something strange when changing the
aperture, as the fstop increases, the aperture
gets smaller.
This seems backward, but that’s because
fstop is a fraction.
This fraction to be exact.
But wait, why go through all this math and
glass when I just said a pinhole keeps everything
perfectly sharp.
Well the simple fact is that pinholes are
very small, and they don’t let in a lot
of light.
Going back to Michael’s video for a second,
you can see how an out of focus image comes
from receiving light from multiple points
on the image sensor from the same point on
an object, and that’s very not good.
What lenses allow us to do is take much more
light in, but bend it so that there is still
a one-to-one relationship between a point
on the object and a point on the sensor.
Of course that sensor can be anything, like
your eyeball.
Your eye has a very similar structure to a
prime lens, so it can’t zoom, but it’s
very good at focusing light onto the retina.
Your cornea, lens and retina mimic a camera
lens almost exactly, but instead of moving
the lens back and forth like in a camera,
it stretches and squeezes.
Those with near or far sightedness have a
problem with one or more of the mechanisms
that should allow their eyes to focus, like
the lens unable to change shape correctly
or the cornea being warped in some way.
So there's some info for you on lenses.
I think lenses are so incredibly cool.
Because, little side note, this may not be
that interesting to you but it is to me
When you buy a set of lenses, a lot of the
time they have to color match
the glass, because the glass can actually
change the look or the color that you see
on the image
So most times when you buy really nice lenses
The entire set of lenses is color matched
so if you switch from like a 14mm to a 25mm
So on and so forth
they all still look the same even though the
distance that it's showing is different
but the color will match.
and that's important because again there are
so many lenses in just one of these lenses
Anyway I could go on forever about lenses.
I love them.
I think they're so so neat, and just so wonderful,
like what a crazy invention.
But, that's for another time maybe.
You know what's for now.
More DONGs
Right down there!
Ones that we talked about.
Playlist of dongs right over here!
And As Always, Thanks For Watching
