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| Seeing a large image of something small |
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In spite of all technical progress, the eye as the visual organ – in combination with the brain behind it – is the most efficient image-processing system available to date. All the appliances provided by technology are no match for the eye as regards speed and resolution. The structure of the eye is related to that of a camera.
Together with the muscle-adjusted lens (1a), the curved surface of the cornea (1) projects an optical image onto the retina (2). The amount of incident brightness is controlled via the variable diameter of an iris (3). A sharp image is provided by the flexible lens, the focal length of which is changed by muscles in such a way that focusing is possible on any subject at a distance between approx. 20 cm and infinity. The image itself is picked up on the retina by approx. 130 million receptor rods (recognition of grey levels) and 7 million cones (color recognition) and transferred to the brain on the shortest possible path via the optic nerve(4).
The light rays shown in the illustration form a viewing angle of 30°. The following objects, for example, are seen under this angle:
- the spire of the Ulm Minster with a height of 161 m, seen from a distance of 300 m
- a photo with a height of 13 cm seen from a distance of 25 cm.
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