1 00:00:00,680 --> 00:00:03,880 Speaker 1: I'm Kristin Conger and I'm Caroline Irvan, and we're hosts 2 00:00:03,880 --> 00:00:06,680 Speaker 1: of the podcast Stuff Mom never told you that gets 3 00:00:06,720 --> 00:00:10,240 Speaker 1: down to the business of being women from every imaginable angle. 4 00:00:10,520 --> 00:00:14,400 Speaker 1: That's right. Kristen and I skillfully decode the biology, psychology, 5 00:00:14,480 --> 00:00:18,000 Speaker 1: and sociology of ladies and gents from their evolutionary past 6 00:00:18,040 --> 00:00:21,880 Speaker 1: a millennial present to better understand all of that stuff. 7 00:00:22,000 --> 00:00:25,400 Speaker 1: Mom never told you. No offense moms, Now be sure 8 00:00:25,400 --> 00:00:32,760 Speaker 1: to subscribe wherever you get your podcasts. Welcome to brain 9 00:00:32,800 --> 00:00:41,200 Speaker 1: Stuff from How Stuff Works. Hi, brain Stuff, I'm Christian Sager, 10 00:00:41,280 --> 00:00:43,320 Speaker 1: and I'm here to talk to you about why people's 11 00:00:43,400 --> 00:00:48,239 Speaker 1: eyes sometimes appear red in photos. Horrible glowing red, the 12 00:00:48,280 --> 00:00:51,279 Speaker 1: glow of eyes that have peered into the abyss and 13 00:00:51,440 --> 00:00:55,720 Speaker 1: through which the abyss peers back. I'm just kidding. It's 14 00:00:55,800 --> 00:00:59,000 Speaker 1: it's just simply a reflection. Everything that you can see 15 00:00:59,160 --> 00:01:02,000 Speaker 1: is reflecting some amount of light. You can see my 16 00:01:02,040 --> 00:01:05,240 Speaker 1: shirt because it's reflecting wavelengths of light and absorbing the 17 00:01:05,280 --> 00:01:08,760 Speaker 1: other wavelengths. Black things like my soul or I guess 18 00:01:08,800 --> 00:01:12,080 Speaker 1: my pupils absorb most of the light that hits them. 19 00:01:12,120 --> 00:01:16,360 Speaker 1: Most pupils look black because they're shadowy windows to the retina. 20 00:01:16,720 --> 00:01:19,840 Speaker 1: The retina is lined with a dark pigment melanin to 21 00:01:19,920 --> 00:01:24,520 Speaker 1: promote light absorption. That gives all the photosensitive cells in 22 00:01:24,560 --> 00:01:27,520 Speaker 1: the retina the best chance at catching the light coming 23 00:01:27,640 --> 00:01:31,800 Speaker 1: at them. The retina contains a lot of those photosensitive cells, 24 00:01:31,880 --> 00:01:36,320 Speaker 1: some one hundred and seven million of them, plus nerves 25 00:01:36,360 --> 00:01:39,240 Speaker 1: to carry messages from those cells back to the brain. 26 00:01:39,760 --> 00:01:43,680 Speaker 1: All that stuff needs blood to function, so the retina 27 00:01:43,720 --> 00:01:47,040 Speaker 1: is also dense with blood vessels. Red eye is just 28 00:01:47,160 --> 00:01:50,640 Speaker 1: a glimpse at those blood vessels. You see. Camera flashes 29 00:01:50,720 --> 00:01:54,640 Speaker 1: illuminate everything within their reach, including the blood vessels in 30 00:01:54,680 --> 00:01:57,960 Speaker 1: the retina. A camera with a built in flash will 31 00:01:58,000 --> 00:02:01,680 Speaker 1: have that flash pointed direct at the subject at the 32 00:02:01,800 --> 00:02:04,560 Speaker 1: speed of light. The flash bounces off the subject and 33 00:02:04,720 --> 00:02:07,360 Speaker 1: back to the lens. If the angle is just right, 34 00:02:07,720 --> 00:02:11,040 Speaker 1: you wind up looking like a minion of zool. Part 35 00:02:11,040 --> 00:02:14,040 Speaker 1: of the problem is that you're using a flash you're 36 00:02:14,080 --> 00:02:17,800 Speaker 1: in dim light, meaning that your subjects irises will be 37 00:02:17,880 --> 00:02:22,360 Speaker 1: dilated with lots of retina showing. Traditional built in flashes 38 00:02:22,400 --> 00:02:26,360 Speaker 1: go off near simultaneously with the shutter way too fast 39 00:02:26,480 --> 00:02:29,920 Speaker 1: for your iris is to contract. That's why some newer 40 00:02:29,960 --> 00:02:33,400 Speaker 1: flashes go off twice, once right before the picture snaps 41 00:02:33,400 --> 00:02:36,359 Speaker 1: to make your eyes adjust, and then again to illuminate 42 00:02:36,360 --> 00:02:39,320 Speaker 1: the scene. You can also prevent red eye by controlling 43 00:02:39,360 --> 00:02:42,280 Speaker 1: the angle of the light. Use a separate flash positioned 44 00:02:42,320 --> 00:02:45,800 Speaker 1: a few feet away from the camera, and try bouncing 45 00:02:45,840 --> 00:02:48,760 Speaker 1: the light off a nearby surface instead of pointing it 46 00:02:48,840 --> 00:02:56,360 Speaker 1: directly at your subject. Check out the brain stuff channel 47 00:02:56,400 --> 00:02:58,520 Speaker 1: on YouTube, and for more on this and thousands of 48 00:02:58,520 --> 00:03:14,639 Speaker 1: other topics, visit how stuff works dot com.