What causes red-eye in photos taken with flash?

• A. Light reflecting back from the retina
• B. Lens flare
• C. Sensor dust
• D. Chromatic aberration

Answer: (A)

Red-eye happens when flash lights the eye in a dark scene, causing the pupil to dilate. The flash light enters the pupil, travels to the retina at the back of the eye, and then reflects off the retina back through the pupil toward the camera. The retina’s network of blood vessels gives that returned light a reddish color, so the pupil area looks red in the photo.

What sets this apart from the other phenomena: lens flare is stray reflections inside the lens itself that create bright spots or haze, not the red color coming from the eye. Sensor dust shows up as dark spots on the image, not a reddish glow. Chromatic aberration appears as color fringes around high-contrast edges due to the lens dispersing different colors differently, not a red reflection from the eye.