Why do photos have red eyes?

Pupil dilation allows more light to pass through, so the blood vessels in the retina will be red in the photo.

When the flash illuminates the human eye, the pupil will be enlarged to let more light pass through, and the blood vessels in the retina will be reddened in the photo. Because the degree of red-eye phenomenon is determined by the depth of pigment in the subject, if the subject's eyes are darker, the red-eye phenomenon will not be particularly obvious.

Ways to reduce red eye:

1. Put yourself in a position with a light source. When you shoot, the pupil of the subject will not be enlarged by strong light stimulation because of the illumination of ambient light.

2. Don't shoot with a flash in a particularly dark place. After turning on the red-eye elimination system, try to ensure that the subject is aimed at the lens and shoot in a place with sufficient light, so that the pupil will remain in a natural state.

3. Use an advanced flash with adjustable angle. When shooting, the flash should not be parallel to the lens direction, and move upward at an angle of 3 degrees with the lens, which can effectively prevent the pupil from being stimulated and enlarged.

4. Create a suitable light source or decide what kind of situation has the best shooting light.

Extended information:

What many cameras can do is to reduce the influence of red-eye phenomenon to some extent. Of course, some cameras do well, but red-eye phenomenon still exists.

For animals, the phenomenon of red eye is different. It is common in domestic animals. Pets' eyes usually have a reflective layer at the bottom of retina, which can enhance their visual ability at night.

The reflective layers of these eye membranes are different from the fur color of the animals themselves, so the phenomena that appear under the stimulation of the flash will be different. For example, if a black animal has a green radiation layer, then it is not a red eye phenomenon, but a green eye phenomenon. Some animals don't have the radiation layer of the eye membrane, so they will have the same red eye phenomenon as humans under the flash.

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