What Kind of Lens is Used in a Magnifying Glass?

What type of lens is used in magnifying glass

A magnifying glass, also known as a hand lens, is an optical instrument that makes small objects appear larger. It uses a special kind of lens that is spherical on both sides. The lens is called a bi-convex lens or simply convex lens. By using refraction, the convex lens makes the image seem closer than it actually is.

In this article, we will briefly discuss a special kind of convex lens called the bi-convex lens that is used in a magnifying glass.

Convex Lens

A convex lens is the simplest type of lens. It produces an enlarged image of an object or focus light from a distant source into a smaller spot on the axis. Convex lenses are widely used in optical instruments such as cameras and binoculars. They are the main component of the magnifying glass. We also see them in items like reading glasses and telescopes.

A convex lens is a single thin lens that bulges out in its center, thus creating a bowl-like shape that can be thinner towards the edges while keeping its center thick.

There are three types of convex lens:

  1. Plano-convex lens
  2. Concave-convex lens, and finally
  3. Bi-convex lens

A Biconvex lens is used in the magnifying glass.

Different types of convex lens, Plano convex lens, bi-convex lens, and concave-convex lens

Bi-Convex Lens

Bi-convex lenses are lenses with an outward spherical curve on both sides. These types of bifocal lenses can be used to magnify small texts for reading or inspect tiny objects without using higher-powered microscopes.

This lens has two focal lengths, one for each side of the surface. The focal lengths can be the same or different. The focal length describes how far away an object must be for its image to become sharp and clear to see effortlessly. 

Unlike microscopes or other optical instruments, the focal length of magnifying glass can not be changed in real-time. To get our desired magnification and clear view of the object under inspection, we adjust the position of our magnifying glass depending on what we want to view to see it clearly.

For example, if you want to see something close up like your hand, you would place it near enough so that objects appear larger than normal and clear to inspect. However, it has some limitations. The image looks blurry around the borders of the lens because they are out of focus. By increasing the size of the lens, we can see a larger area of the object clearly.

Light converging to a point through a biconvex lens in a magnifying glass

Magnification

The magnification power of this lens can also be increased to look at smaller details of tiny objects. It can be increased by increasing the curvature radius of its surfaces. However, too much curvature will result in a lens so thick that it will not be useful.

The type of biconvex lens used in the magnifying glass has a focal length between 30-60 cm or 12-24 inches, depending on its size. Focal length in this range allows people to see objects close up without them looking blurry around the edges.

Biconvex lens of different magnification power by changing the radius of curvature of the surfaces

We often see 2X, 5X, 10X etc., written on the magnifying glass. These numbers are called the magnification of the lens used in the magnifier. How much the lens could magnify the actual object is determined by a simple mathematical formula. The formula depends on the distance of the actual object and its image from the lens. 

The formula is as follows:

Magnification = Image distance/Object distance

Illustration of magnification of object in a magnifying glass. Image distance and object distance is used to calculate magnification

Working Principles

The human eye only collects a small amount of light from a tiny subject, making it difficult to see. By using lenses with different shapes and sizes, magnifying glasses can increase this captured light allowing us to see objects as if they were larger than life. 

A common misconception is that you look through them like binoculars, but actually, your eyes are still focused at infinity when looking through the object instead of crossing over like when viewing something close up. 

Bi-Convex lenses work by refracting light in a way that causes the rays to converge to a point. Because of its unique design, the lens captures more light from the smaller object and converges them together so that they can enter into our eyes. 

Illustration of magnification of object with a magnifying glass

Our cornea collects the converged rays. They pass through the lens inside our eye. The lens in our eyes can adjust its focus so that a clear image is formed on our retina, and we see an enlarged image of the object by using a bi-convex lens. 

You can find a detailed explanation about the working principle in our article “How Does a Magnifying Glass Work?”. Please see the following video to know more about how images are formed inside our eyes. 

Conclusion

A magnifying glass is a device that uses bi-convex lenses to make an object look larger. The lens has two surfaces curved outward from each other like an egg. One surface bends light rays coming from distant objects, while the other focuses on a point.

The magnification power of this lens depends on the curvature radius of this lens. By increasing the curvature, we can increase the magnification power. 

Magnification is another important parameter. We express the magnification of a hand lens by using multiplications like 2X, 5X, 10X, etc. A magnifying glass with 2X magnification creates an image that is twice the size of the original object. Magnification is calculated based on the distance of the actual object and its image from the lens. 

So, what magnification do your magnifiers have? Please let us know in the comment section below.  

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