
Contents
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Mirrors in eyes Mirrors in eyes
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The image-forming reflector in the eye of the scallop The image-forming reflector in the eye of the scallop
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The stepped-mirror eyes of Dolichopteryx The stepped-mirror eyes of Dolichopteryx
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Other mirror eyes Other mirror eyes
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Tapeta Tapeta
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Reflecting sunshades Reflecting sunshades
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Anti-reflection coatings Anti-reflection coatings
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The physical optics of animal reflectors The physical optics of animal reflectors
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Uses of photonic reflectors in structures other than eyes Uses of photonic reflectors in structures other than eyes
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Display Display
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Reflecting camouflage Reflecting camouflage
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Summary Summary
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Cite
Abstract
A small number of eyes employ concave mirrors, rather than lenses, as image-forming structures. The most impressive of these is in the scallop Pecten, where the image in each of the 60–100 eyes provides a means of detecting movement. Image-forming mirrors are also found in the secondary eyes of the deep-sea spookfish Dolichopteryx and the deep-sea ostracod Gigantocypris. Reflecting tapeta that do not form images, but which double the effective light path through the retina, are common in vertebrate eyes and also in the compound eyes of some insects and crustaceans. Some insects, particularly lepidoptera, have anti-reflection coatings on their eyes that consist of an array of minute nipples. These serve to minimise the refractive index transition from air to chitin. Reflecting structures can be classified according to their structure as one-dimensional (plates), two-dimensional (rods), or three-dimensional (solid or hollow spheres). Most animal mirrors employ the principle of multilayer interference from stacks of plates of alternating refractive index. Materials involved in biological multilayers include guanine and cytoplasm (fish scales), and chitin and air (insect wings). The highest reflection is produced when the refractive index difference is high. Because the reflectance of a multilayer is a function of wavelength, most biological reflectors are coloured, which makes them useful in display. The special light conditions in the ocean make it possible to use mirrors as an effective form of camouflage. The silvery scales disguise the sides of the fish, by reflecting light that is close in brightness to the background.
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