While human eyes are extraordinarily sophisticated biological organs and photographic cameras are mechanical objects which can be constructed fairly simply, eyes and cameras have some essential similarities in the ways they work. This is not surprising since the basic physics of light and optics determine the fundamental functional structures of both these systems.
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A Dark Room
Eyes and cameras work both rely on a volume of space surrounded by a barrier that is opaque to light except for one opening, which allows the controlled entry of light into the space. The word "camera" comes from a Latin word meaning "a vaulted room." Some of the first photographic devices were called "camera obscura," which means "dark room" in English. While the human eye is roughly spherical in shape and cameras usually have a rectangular form, both can be considered dark rooms of softs. The volume of a human eye is surrounded by the opaque material of the white---or sclera---of the eye. A camera also requires an opaque material, typically wood, metal or plastic, to surround its volume of space to form the body of the camera. Both cameras and eyes have openings at one end of the space. The eye has a pupil, and the camera has an aperture.
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For light to be captured in a way that forms an organised visual image inside of the space of the camera or inside the eye, its entry must be controlled. This is achieved by having one opening, or diaphragm, called a pupil for the eye and an aperture for a camera, at one side of the enclosed space. Both the pupil and typical camera apertures can change diameter, allowing smaller openings that let in less light in bright situations or larger openings that let in more light in dim situations. The light then travels in a controlled quantity through the opening and is projected on the opposite side of the space.
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Focusing the Image
If the opening, or diaphragm, is very small, a fairly clear image will be projected on to the surface of the enclosed space opposite the diaphragm. This opening will generally be too small to allow in enough light unless the light is very bright. If the opening is enlarged to let in more light, the resulting projected image becomes proportionally less clear or unfocused as the diameter of the diaphragm is increased. Therefore, a lens is needed to gather the light that comes through diaphragms large enough to work in most circumstances and bring the image into focus. Both camera and eyes have lenses. The lens in the human eye is flexible, and its focus is controlled by muscles in the eye. Camera lenses are rigid, and the focus is controlled by varying the distance between the object being focused on and the image projection plane.
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Capturing the Image
Once the light rendering an object has passed through the diaphragm with the control of the aperture and is brought into focus by a lens, the image must be captured by a light-sensitive substance on the image plane. This is accomplished with the biochemical reactions in the retina of an eye and by film or a digital sensor in a camera. This light-sensitive substance is located at the focal point of the lens on the opposite surface of the dark space from the diaphragm.
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The most fundamental yet seldom-mentioned aspect in the way both cameras and eyes work is in their reliance on the brain to direct their operation and interpret the visual information they capture. The saying "Every picture tells a story" is not exactly true. In fact, the human mind makes up stories about pictures when a person looks at them. People must choose what to look at or where to point a camera and the brain must assign meaning and value from the visual information communicated through the image.