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Optical instruments are any equipment that uses a single or several lenses to take in light as an input and perform any action on it, depending on the equipment's purpose, to either enhance an image for clearer viewing or enlarge it. Popular optical instruments all make use of one type of lens or the other.

The first optical instruments to be used were the earlier versions of telescopes, developed when the need to study the planets and their moons and other celestial bodies were on the rise. The invention of the first telescope is credited with the Italian astronomer and physicist Galileo di Vincenzo Bonaiuti de' Galilei, commonly referred to as Galileo Galilei, who is considered the Father of Observational Astronomy.

Another popular optical instrument is the microscope, which is used to look at very small particles and organisms. The very first microscope was invented by a Dutch eyeglass maker named Zacharias Janssen. Owing to his intensive research in the field of microscopy, the Dutch scientist Antonie Philips van Leeuwenhoek is considered the Father of Microbiology. Both the telescope and microscope work on the idea of image enhancement, where a minute object is enlarged so that it can be looked at and studied with much ease.

Apart from the instruments that are useful in enlarging an image, another class of optical instruments help in analyzing the properties of light or optical materials. Some of these optical instruments are mentioned below:

  • Interferometer – meant for the measurement of the interference properties of light waves
  • Photometer – helps in the measurement of light intensity
  • Polarimeter - measures the dispersion or rotation of polarized light
  • Reflectometer – helps in the measurement of the reflectivity of a surface or object
  • Refractometer - measures the refractive index of various materials
  • Spectrometer or Monochromator – meant for the generation or measurement of a portion of the optical spectrum, for chemical or material analysis
  • Autocollimator – helps in the measurement of angular deflections
  • Vertometer - used in the determination of refractive power of various types of lenses

Examples of Optical Instruments

Telescopes: Telescopes consist of either lenses or curved mirrors, or sometimes both to help observe faraway objects or celestial bodies. Telescopes can also be used to observe distant objects as a measure of their emission, absorption, or reflection of electromagnetic radiation. Telescopes are commonly and primarily used in the field of astronomy. Although the first telescope invented was a refracting telescope, much better versions of it called reflecting telescopes are now predominantly used. Refracting telescopes make use of lenses, whereas reflecting telescopes make use of curved mirrors to form an image. Although the term "telescope" refers to optical instruments that deal with the waves in the electromagnetic spectrum, several modern telescopes also deal with waves of different wavelengths. Some are mentioned below.

  • X-ray telescopes – deals with waves having wavelengths shorter than ultraviolet light
  • Ultraviolet telescopes – waves with shorter wavelengths than visible light
  • Optical telescopes – meant for only visible light
  • Infrared telescopes – waves with longer wavelengths than visible light
  • Submillimeter telescopes – meant for microwave wavelengths that are longer than those of infrared light
  • Radio telescopes – meant for waves with even longer wavelengths than infrared light

Eyes: The most important organ of the visual system in all animals alike, the eyes, is a great example of an optical instrument. Humans have a complex pair of eyes that are advanced compared to other animals, as our eyes can distinguish between different shapes, colours and contrasts.

Binoculars: Also called field glasses, binoculars consist of two refracting telescopes mounted side-by-side in a single frame so that when looked through the peeping hole, it allows a single image of a distant object to fall on the eyes of the perceiver. Unlike telescopes, binoculars allow the user to use both their eyes.

Magnifying glass: A very simple example of an optical instrument, magnifying glass, also called a hand lens, makes use of primarily two components.

A convex lens is used to enlarge and observe rather small objects and writings. A frame that can be held on to when using the magnifying glass.

Since it makes use of a convex lens, which produces a focused image, a magnifying glass can also be used to concentrate all the sunlight that falls on it onto a particular spot to create a fire.

Eyeglasses: Another common type of optical instrument found in everyday life are eyeglasses, commonly referred to as spectacles. Depending on the condition of the user (myopia or hypermetropia), specific eyeglasses can be manufactured and used to make up for the defect in the user's vision.

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