Optical Instruments: Definition, Types and Examples

Optical Instruments is an important topic of Physics. In order to form new or sometimes altered images, light waves can be bent and reflected. The analysis of how light rays can be manipulated allows us to create better fiber optic cables, contact lenses and high powered telescopes. The instruments that are formed by using the reflecting and refracting properties of spherical mirrors, lenses, prisms are the optical instruments. These are the instruments that process light waves or photons either to determine the characteristic properties of an image or to enhance an image for viewing. We use several optical instruments in our day to day lives.

Key Takeaways: Optical Instrument, eye, simple microscope, compound microscope, telescopes, mirror

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Optical Instruments- Definition

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The human eye is an incredible organ that enables us to see the world around us. The reason we can view and interpret objects is because of the light that they reflect. Light has always been known to travel at a very high speed, and today we know that the speed of light in vacuum is c = 3 × 10⁸ m s^–1 . This is the highest possible speed of light achievable. This chapter deals with the various optical instruments, the most important of them being the eye. 

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The Eye

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The structure of Eye

The image above is that of the structure or the anatomy of the eye. The white part of the eye which is visible from outside is a protective shield called the Sclera. The visible circular part is called the iris, the colour of which changes from person to person and the centre part of the iris is called the pupil. The iris controls the amount of light that goes in through the pupil and accordingly adjusts the size of the pupil. For example, when one is out in the sun, the pupil contracts and becomes smaller to let in small amounts of light but the opposite happens when one is indoors. 

The light which enters from the pupil goes to the retina which has something known as rods and cones that allow us to detect colour. The cornea first refracts the light entering the eye, which is then incident on the iris. The lens is right behind the iris and forms images that shape our worldview. 

Defects of the Eye

As a person ages, the ability to see things clearly also diminishes and this is called presbyopia. It is corrected by using a converging lens. Another defect is hypermetropia or far sightedness in which the person can see far off things clearly but not the closer ones. This is corrected using a convex lens. Myopia is the opposite of hypermetropia.

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A Simple Microscope or Magnifying Microscope

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Another optical instrument is the simple microscope whose main function is to allow us to see small objects. 

Magnifying power of a simple microscope 

A simple microscope, which is also known as a magnifying glass, is a convex lens with a short focal length and allows us to see small objects in a magnified manner. As a result, when it is held near the eye magnified, an erect or virtual image is formed.

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A Compound Microscope

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Compound microscope

A compound microscope is called so because it involves the use of 2 convex lenses to see extremely small objects like microorganisms. It consists of an eye piece, an objective lens and an adjective screw. It allows users to adjust the focal length as per the object of observation.

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The Telescopes

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While a microscope is used to observe minute objects, a telescope is used to see far off objects which are large. It is primarily of 2 types - reflecting and refracting. A reflecting telescope does not use a lens, instead it uses concave mirrors to focus the light.

A refracting telescope uses 2 lenses to focus on the light and magnify the object to make it look closer than it is. Since convex lenses work by bending light inwards, they are used in refracting telescopes.

A Refracting Telescope

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Things to Remember

• The human eye is an incredible organ that enables us to see the world around us.
• The white part of the eye which is visible from the outside is a protective shield called the Sclera. The visible circular part is called the iris, the colour of which changes from person to person and the center part of the iris is called the pupil.
• The iris controls the amount of light that goes in through the pupil and accordingly adjusts the size of the pupil.
• As a person ages, the ability to see things clearly also diminishes and this is called presbyopia.
• Another optical instrument is the simple microscope whose main function is to allow us to see small objects.
• A refracting telescope uses 2 lenses to focus on the light and magnify the object to make it look closer than it is.

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