Why does flash photography cause red eyes | Love playing computer games - 上海419贵族宝贝-上海后花园1314-上海品茶网-阿拉爱上海

When people take portraits at night, because the environment is too dark, in order to supplement the light, most people will choose to turn on flash photography. But after shooting, the figure is clear, but why does the pupil of the human eye turn into a horrible red? Remember that the wheel eye only exists in the second dimension.

In fact, the pupil of a person, like the aperture of a camera, can be adjusted, but its size and response are jointly controlled by the sympathetic nerve and parasympathetic nerve. They coordinate and interact with each other to complete the change, which cannot let us do as we want. In dark places, the pupil will automatically enlarge to see the scenery clearly.

When taking photos with flash light, strong light comes in a flash, and the iris has no time to close the pupil tightly. The light passes through the congestion zone called choroid near the iris and reaches the retina, where the blood vessels are also very rich. Some light is reflected back and captured by the lens, causing the pupil in the picture to be red.

Interestingly, if you take pictures of animals at night, you may get some other "eyes", for example, some dogs will have "green eyes". This is because the bottom of the dog's retina has a green reflective layer that can enhance their night vision ability.

Now some mobile phones have a "red eye prevention" mode in the flash mode, or the default flash mode is this red eye prevention mode. When taking photos in this mode, the flash will pre flash several times to stimulate the pupil contraction before taking the lens, so that the photos will not have red eye phenomenon. Or you can choose an ingenious angle so that the flash will not directly penetrate your eyes (such as squint).