Optical Instruments

Optical instruments are devices which use light rays for one of two purposes.

  1. Enhancement of Images for Viewing
  1. Analysis of Light to determine different characteristic properties

Enhancement of Images

The most common types of optical instruments in this category are microscopes and astronomical telescopes.

Astronomical telescopes are used to magnify distant objects in order to see them clearly.There are of three types of Astronomical telescopes

  1. Refracting telescopes: These use a combination of lenses to form a magnified image
  2. Reflecting telescopes: These instruments use a combination of mirrors to form a magnified image
  3. Catadioptric telescopes: These instruments use a combination of both lenses and mirrors to form images

Other than these three main types of optical telescopes, there are many others classified according to their varying tasks.

Microscopes are instruments designed to magnify small objects. A simple microscope uses only one lens for the sake of magnification whereas a compound microscope uses more than one lens. A compound microscope uses two lenses, one as the objective and the other as the eyepiece.

The camera is another type of optical instrument. The objective is a converging lens. Light from a distant object is refracted through the objective lens and when the film is “exposed” the light for the short span, the image is etched onto it. Digital camera do not use films however. The image in this case is captured by image sensors and reproduced in the many number of ways available.

Slide and film projectors are other examples of optical instruments. The image is illuminated and by using a combination of lenses magnified and projected onto a screen where it is displayed. Simple tools like magnifying lenses are also optical instruments.

Analysis of Light

Instruments like photometers (used to measure light intensity), polarimeter (used to measure rotation of polarized light) and others are used to measure different characteristics of light waves. For example, a refractometer is used to measure the measure the refractive index of various materials when light passes through it.

Learn about different types of optical instruments and their working principles with the help of our expert tutors here at BYJU’S.


Practise This Question

The magnifying power of a microscope with an objective of 5 mm focal length is 400. The length of its tube is 20 cm. Then the focal length of the eye-piece is          [MP PMT 1991]