WEBVTT - What Causes Red Eye In Photos?

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<v Speaker 1>I'm Kristin Conger and I'm Caroline Irvan, and we're hosts

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<v Speaker 1>of the podcast Stuff Mom never told you that gets

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<v Speaker 1>down to the business of being women from every imaginable angle.

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<v Speaker 1>That's right. Kristen and I skillfully decode the biology, psychology,

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<v Speaker 1>and sociology of ladies and gents from their evolutionary past

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<v Speaker 1>a millennial present to better understand all of that stuff.

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<v Speaker 1>Mom never told you. No offense moms, Now be sure

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<v Speaker 1>to subscribe wherever you get your podcasts. Welcome to brain

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<v Speaker 1>Stuff from How Stuff Works. Hi, brain Stuff, I'm Christian Sager,

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<v Speaker 1>and I'm here to talk to you about why people's

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<v Speaker 1>eyes sometimes appear red in photos. Horrible glowing red, the

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<v Speaker 1>glow of eyes that have peered into the abyss and

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<v Speaker 1>through which the abyss peers back. I'm just kidding. It's

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<v Speaker 1>it's just simply a reflection. Everything that you can see

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<v Speaker 1>is reflecting some amount of light. You can see my

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<v Speaker 1>shirt because it's reflecting wavelengths of light and absorbing the

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<v Speaker 1>other wavelengths. Black things like my soul or I guess

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<v Speaker 1>my pupils absorb most of the light that hits them.

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<v Speaker 1>Most pupils look black because they're shadowy windows to the retina.

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<v Speaker 1>The retina is lined with a dark pigment melanin to

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<v Speaker 1>promote light absorption. That gives all the photosensitive cells in

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<v Speaker 1>the retina the best chance at catching the light coming

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<v Speaker 1>at them. The retina contains a lot of those photosensitive cells,

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<v Speaker 1>some one hundred and seven million of them, plus nerves

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<v Speaker 1>to carry messages from those cells back to the brain.

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<v Speaker 1>All that stuff needs blood to function, so the retina

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<v Speaker 1>is also dense with blood vessels. Red eye is just

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<v Speaker 1>a glimpse at those blood vessels. You see. Camera flashes

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<v Speaker 1>illuminate everything within their reach, including the blood vessels in

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<v Speaker 1>the retina. A camera with a built in flash will

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<v Speaker 1>have that flash pointed direct at the subject at the

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<v Speaker 1>speed of light. The flash bounces off the subject and

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<v Speaker 1>back to the lens. If the angle is just right,

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<v Speaker 1>you wind up looking like a minion of zool. Part

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<v Speaker 1>of the problem is that you're using a flash you're

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<v Speaker 1>in dim light, meaning that your subjects irises will be

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<v Speaker 1>dilated with lots of retina showing. Traditional built in flashes

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<v Speaker 1>go off near simultaneously with the shutter way too fast

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<v Speaker 1>for your iris is to contract. That's why some newer

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<v Speaker 1>flashes go off twice, once right before the picture snaps

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<v Speaker 1>to make your eyes adjust, and then again to illuminate

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<v Speaker 1>the scene. You can also prevent red eye by controlling

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<v Speaker 1>the angle of the light. Use a separate flash positioned

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<v Speaker 1>a few feet away from the camera, and try bouncing

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<v Speaker 1>the light off a nearby surface instead of pointing it

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<v Speaker 1>directly at your subject. Check out the brain stuff channel

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<v Speaker 1>on YouTube, and for more on this and thousands of

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<v Speaker 1>other topics, visit how stuff works dot com.