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| Prisms – Key Optical Components |
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Apart from optical lens elements, practically no other optical component plays as important a role in determining the performance of an optical instrument as the prism. Depending on their effect and application, prisms can be classified as refracting prisms, dispersion prisms, polarizing or reflection prisms.
Examples of prism applications
Prisms can be used as mirrors to reflect light, but they also sometimes serve to refract light. If they consist of birefringent materials (i.e. materials which refract light in two slightly different directions to form two rays), they can separate polarized light into partial rays known as ordinary and extraordinary rays. This effect is utilized in numerous optical instruments. In microscopes, prisms are required for Differential Interference Contrast –
DIC in incident light and DIC in transmitted light. When used as components in refractometers, they serve to measure the refractive index of solid or liquid materials with the aid of total reflection.
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| The optics of the Victory 8x56 B T* binoculars from Carl Zeiss. | Ray path in prismatic eyeglass lenses. | Sugar refractometer from Carl Zeiss, 1923. |
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Careful prism arrangement makes it possible to produce extremely compact binoculars. One prime example of this is pocket binoculars. Eyeglass lenses with integrated prisms are used to compensate for defects in binocular vision, e.g. for the correction of heterophoria or heterotropia, known as ”squinting” by the layman. In squinting, the imaging rays are deflected in front of the abnormally fixating eye in such a way that a normal image is generated on the retina despite the deviant line of sight.
Refractometers from Carl Zeiss
In 1874, the Abbe refractometer was developed at Carl Zeiss in Jena on the basis of work and practical experience with Wollaston’s and other prisms. Product enhancement led to special forms which were very suitable for rapid measurement of the refractive indices of liquids. The butter and milk fat refractometer was created in 1893. With the introduction of the Pulfrich refractometer some years later, an instrument became available which not only turned out to be very practical for laboratory work, but was also very exact. It also allowed the refractive index measurement of pulverized solid bodies. A further simplified form of the Abbe refractometer was the Pulfrich immersion refractometer presented in 1899.
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| Prisms – Key Optical Components |
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