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  • 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 differentlenses

  • 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 constantwell 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 anafocal 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

Hello there, my name is Jake Roper

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    林宜悉 發佈於 2021 年 01 月 14 日
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