D) They watched the sky with only the naked eye.
101. RED-EYE EFFECT
Have you ever taken a perfect picture - and then noticed that everyone’s eyes were glowing red? Why do our
eyes sometimes look red in photographs? It is an effect that happens when a flash is used. Under normal
conditions, the eye’s iris contracts in bright light.
This makes the pupil small, and does not let much light into
the eye. When a flash is used, however, conditions are different.
When a flash goes off, the iris does not have
enough time to react. Thus, the pupil stays wide open for the photo. The flash is so bright that some of
its light reflects off
the retina, a layer of cells at the back of the eye. Because of all the blood vessels in the
retina, the light that it reflects is red. This is why the pupil appears red in the photo. The red-eye effect is not
as easy to notice in everyone. For example, people who are not standing directly in front of the flash are not as
susceptible to the effect.
In addition, there is a natural variety in how the pupil reacts to changing light
conditions. Some people have pupils that become very wide. These people are more likely to experience the
red-eye effect. Those who have smaller pupils are less likely to experience it.
The red-eye effect can be
reduced by backing away from the subject of the photograph. The further the camera is from the retina, the
less reflected light it will detect. New cameras come with a special “red-eye reduction” setting, which causes
the camera to flash twice instead of once. The first flash
shrinks your pupil, and the second takes the photo.
The smaller your pupil, the less red light it will reflect back to the camera.
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