• 3 months ago
Transcript
00:00Ooh, old-timey photographs!
00:14How much?
00:15Five bucks.
00:16Well, you got it.
00:17I don't believe this is the only costume you had left.
00:26Dear Tim and Moby,
00:31How are our eyes able to see stuff?
00:34I don't get it.
00:35Sincerely, Fausto.
00:37Well, believe it or not, your eyes work kind of like a film camera.
00:41Light tends to move in a straight line unless something reflects it or bends it.
00:46When light hits an object, it bounces off and is reflected into your eyes.
00:51Your eyes have their own light-bending parts called the lens and cornea.
00:55The cornea is the outermost part of the eye.
00:58It collects all the light that's bouncing off of objects and focuses it through a small hole.
01:03That's your pupil, the black spot we all have at the center of our eyes.
01:08The iris, or colored part of your eye, opens and closes around the pupil, depending on how much light there is.
01:14If it's dark, the pupil will open up wide to let in as much light as possible.
01:20Whoa.
01:25Right behind the pupil is the lens, which focuses light onto the back of your eyeball.
01:30The lens is clear and curved, and it can change its shape depending on what you're trying to focus on.
01:36It acts a lot like the lens of a camera.
01:39The back of the eye is coated with a special layer of tissue called the retina.
01:43The retina is kind of like the film in a camera.
01:46It's covered in photoreceptive nerve cells.
01:50Oh, photoreceptive just means they're sensitive to light.
01:54Anyway, there are two kinds of photoreceptors on the retina.
01:57You've got about 6 or 7 million cones and more than 120 million rods.
02:03Rods are very sensitive to light.
02:05In fact, they can be triggered by a single photon.
02:08The cones are less light-sensitive.
02:11But unlike the rods, they can detect color.
02:19No, I am not posing for color pictures.
02:22So the lens projects an image onto your retina,
02:25where the rods and cones transform the light and color into electrical impulses.
02:30These are transmitted up your optic nerve and into your brain.
02:34There, your brain decodes the image, and that's how you see.
02:38Right, there's another way the eye is like a camera.
02:41When a camera lens focuses an image on film, it winds up upside down.
02:46And when the lens of your eye focuses an image on your retina, it also turns upside down.
02:51But when your brain processes the image, it flips it right side up for you.
02:56If that didn't happen, well, you'd probably fall down a lot more often.
03:01I'm glad you asked.
03:03Humans have pretty good vision, but some animals can see even better.
03:07Raptors, like eagles and hawks, have eyesight ten times as sharp as ours.
03:12They can see their prey from a thousand meters up in the sky.
03:16And believe it or not, the eyes of the giant squid are a lot like ours, with millions of rods and cones.
03:24Okay, can I have my photo now, please?
03:31I want my five bucks back.