What causes "Red Eye" in photos? Why do some people always have it and some people never do?

The red eye effect is simply the light reflecting off of the person’s retina. What you are actually seeing are the blood vessels in the back of the eye that feed the cells of the retina. Red eye reduction in cameras works by shooting a quick flash to constrict the pupil, thereby reducing the flash of light that reflects off of the retina with the second, more powerful flash.

Probably someone else will give a better answer, but I know it has to do with how pigmented someone’s eyes are. If there’s no pigment, the camera can get confused about how to interpret it, so blue-eyed people are the most likely to have red-eye. People with brown-black eyes almost never do.

Lighter-eyed people are more sensitive to light. Light attacks blue-eyes more than brown. Light is always out for a good fight. @shilolo is right about the reflectivity of the retina so the answer relates to how some people always have their pupils flapped open while others keep them clamped shut. This then relates to the war between blue eyes & light, as the blue-eyed will be clampers & the browns will be flappers. If someone is satisfied with life in general, they will tend to flap open their pupils alot & will tend to red-eye. So red-eyed people are the happy ones.

@psyla But I am totally light sensitive, see really well in the dark, my eyes are brown, and I’m clinically depressed.

@loser your clinical depression causes your pupils to clamp shut, not enjoying the beauty of your world. Your brown-eyed genetic defense against light cannot compensate for your dour depressed ambience. You need to live a little. Only then will you become a red-eye.

Babies and people who are drunk take longer for their pupils to contract so often have more red eye than others.

It normally only happens with on camera flashes that are in a direct line with the persons retina. If the flash is offset it doesn’t happen. With a good, sharp lens, you can get a great deal of eye detail, you don’t want the pupil pin-sized, you want it large and appealing. For that reason I prefer not to use a “pre-flash” as it makes people’s eyes look beady. I use either a bounced flash or off camera flash (when flash is needed.)

Some people are good and some are just evil

I concur with @Judi the people with red-eye are drunk. The ones without red-eye are the designated drivers. If you bounce your flash like @DarkScribe said, this will solve the red-eye problem & noone will know that you’re drunk.

Red eye is light reflecting off the retina. You will get it if the flash is near the camera’s lens opening and the person is facing a darker area so their pupils are wide open. Use a remote flash or have the subject face a little more light.

~Of course you will see red eye if they are evil but don’t worry. The photo will completely catch their spirit so you can make the world a better place by burning the photo and your camera later.