What Is a Magnifying Glass?

A magnifying glass is an optical instrument used to enlarge objects so that we can see them better. It focuses light on a small area. We use this tool to examine something closely.

Illustration of a woman holding a big magnifying glass

Invention of Magnifying Glass - Short History

A girl seeing through a magnifying glass

The magnifying glass is an ancient tool. But like most other antique equipment, it didn’t vanish with time. We see lots of usages of magnifiers in our daily life.


Historians believe that this optical device was in use since 800 BC. But this is not proven undoubtedly. The oldest historical proof of using a convex lens as a magnifying device lies in the 10th century. As per the record, an Arabian scholar, Alhazen, first used the magnifying glass to form a magnified image[1].


English philosopher Roger Bacon described the properties of the magnifying glass in the 13th century, which led to the development of eyeglasses later[2]. Most of the scholars thus recognize Roger Bacon as the inventor of the magnifying glass.

  1. Kriss, T. C., & Kriss, V. M. (1998). History of the Operating Microscope: From Magnifying Glass to Microneurosurgery. Neurosurgery, 42(4), 899–907. doi:10.1097/00006123-199804000-00116
  2. Wikipedia Contributors (2019). Magnifying glass. [online] Wikipedia. Available at: Wikipedia.

Working Principle

Magnifying glass uses a convex lens to make things appear more prominent. It is used to produce a magnified image of an object.


When light reflects from an object, the reflected rays travel in a parallel direction to one another. If we place a convex lens in the path of these parallel rays, these rays will pass through the lens and bend. Finally, they will converge to a point situated at one of the focal points of the convex lens of the magnifying glass.


If we look at the object through the opposite side of the glass, our eyes won’t notice the bending of light rays. But, we will feel like the light rays are traveling on a straight path and coming to us from a much bigger object situated at a distant place. We will see a more extensive virtual image of the original object situated behind the object.

Man inspecting with a magnifying glass

Read our article “How Does a Magnifying Glass Work?” to find out more about the working principle of the magnifying glass.

Type of Lens Used

Magnifying glass with a convex lens

A magnifying glass is mainly a simple microscope. Its primary function is to magnify or enlarge objects placed before it. It is composed of a bi-convex lens. This lens is a particular type of glass that is convex on both sides of the lens.

 

We can consider each side of the bi-convex lens as an arc (part of the circumference of a circle). That means both sides of the piece of glass have a center and a radius that could be the same or different. 

 

The center on both sides of the lens is called the primary or principal focus of the magnifying glass. The radii are called the focal length.

 

The magnification power of the magnifier depends on the focal length of the convex lens used in the magnifying glass.

Read our article What kind of lens is used in a magnifying glass to find out more about the function of the bi-convex lens as a magnifier.

How to Use

The process of using magnifying glasses varies from type to type. No one will use the magnifying lamp for soldering and the magnifying loupe for jewelry the same way. Similarly, the processes of using a page magnifier and a magnification dome are different. 


Whatever the intended application is, the principle process of using these optical apparatus remains the same for each type.

  • Place a magnifying glass on the object you are examining. The glass should be between the object and your eye. Hold it as close to your eye as possible.
  • Move the lens in between while looking at the object through the glass.
  • Once you get a clear and satisfactory view of the object, fix the position of the glass. The magnifying glass is now giving you a clear and magnified version of the original object.
Boy seeing through a magnifying glass

Usages of Magnifying Glass

Inspecting a fingerprint with a magnifying glass

A magnifying glass is an essential tool for every home. We use it for various purposes such as reading, sewing, painting, jewelry making, etc. We can even concentrate the sunlight through a magnifying glass to a point and start a fire. 


The magnifier, aka loupe, has two parts:

 

  1. A lens, and
  2. A handle

The lens is usually made of glass or plastic. The handle is constructed with wood, plastic, or metal.

 

We see magnifying glasses of different sizes, shapes, and power for different applications, but their primary function is the same. For example, there are magnifying glasses for reading books, sewing, jewelry making, etc., and there are also magnifying glasses for looking at small objects such as coins, stamps, etc.

A magnifying glass can also be used as a survival kit. You can start a fire with it in the presence of sunlight. Read our article How To Start a Fire With a Magnifying Glass? to know more about it.