An optical instrument either processes light waves to enhance an image for viewing, or analyzes light waves (or photons) to determine one of a number of characteristic properties.

Image enhancement

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The first optical instruments were telescopes used for magnification of distant images, and microscopes used for magnifying very tiny images. Since the days of Galileo and Van Leeuwenhoek, these instruments have been greatly improved and extended into other portions of the electromagnetic spectrum. The binocular device is a generally compact instrument for both eyes designed for mobile use. A camera could be considered a type of optical instrument for storing an image.

Analysis

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Another class of optical instrument is used to analyze the properties of light or optical materials. They include:

• Interferometer for measuring the interference properies of light waves
• Photometer for measuring light intensity
• Polarimeter for measuring dispersion or rotation of polarized light
• Reflectometer for measuring the reflectivity of a surface or object
• Refractometer for measuring refractive index of various materials, invented by Ernst Abbe
• Spectrometer or monochromator for generating or measuring a portion of the optical spectrum, for the purpose of chemical or material analysis.
• Autocollimator which is used to measure angular deflections.

Optical devices