Difference Between Convex and Concave Lens

Edited by Diffzy | Updated on: July 01, 2023


Difference Between Convex and Concave Lens

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The term "lens" refers to a transparent, curved piece of glass or plastic that focuses and refracts light in a specific way. The object's curvature determines how much and in which direction light is bent. They are employed in telescopes, microscopes, and eyeglasses. The lens can be classified as either a convex lens or a concave lens depending on its shape. While the latter spread the parallel beam of light, the former concentrates on it.

Convex Lens Vs Concave Lens

The point of convergence, or point of focus, for a convex lens, is where all the light rays come together, whereas the point of divergence, or point of focus, for a concave lens, is where the light rays appear to diverge.

Difference Between Convex  and Concave Lens (in Tabular Form)

BasisConvex lensConcave Lens
MeaningConvex lenses are those that combine the light rays that pass through them at a certain spot.The lens that scatters the light rays that strike the lenses is known as a concave lens.
Centre and edgesCompared to its edges, it is thicker in the middle.middle that is thinner than its edges.
Focal lengthPositiveNegative
ImageReal and upside-down photograph.A distorted, virtual, and erect image.
Objectslook bigger and closer.appear more distant and smaller.
Used toCorrect HyperopiaCorrect myopia

What is Convex Lens?

Two spherical surfaces often form an optical lens. It is referred to as a biconvex lens or a convex lens if those surfaces are curved outward.  These lenses have a thicker center and a thinner edge.

Additionally, this lens can focus on an outside light beam to a point on the opposite side by converging it. This idea is referred to as the emphasis. The focal length of a convex lens is defined as the distance from the lens's center to the point of focus.

We will refer to it as a plano-convex lens if one of the surfaces is flat and the other is convex. Additionally, because a convex lens converges with a parallel light beam on a point that we refer to as the principal focus, we also refer to them as converging lenses.

Types of Convex Lens

These lenses can be broadly categorized into three categories: plano-convex, double-convex, and concave-convex: -

  1. Plano Convex Lens: - It has a side that curls outward and a plain side on the other. One flat surface and one spherical surface are present in the positive focal length elements. These lenses were created for non-critical applications using infinite parallel light. These optical lenses are also used as general-purpose focusing elements.
  2. Double convex Lens: - outward in a curve on both sides. It is also known as a biconvex lens or simply a convex lens. They also have a lower focal length than plano-convex lenses with the same surface radius and diameter. Double convex lenses are more advantageous due to the need for longer focal lengths in various optical systems. Among other things, we utilize them as a projector, monocular, telescope, and camera. Additionally, it produces the real image for photography as well as the virtual image for the human eye.
  3. Concave Convex Lens: - It slants both inward and outward from one side. We employ it to correct the spherical aberrations brought on by the other lenses. Additionally, we employ it to regulate the laser beam. To put it another way, it combines one convex lens and one concave lens.

Uses of Convex Lens

In our daily lives, we employ these kinds of lenses for a variety of tasks: -

  1. The lens in a person's eyes is one example. The most typical way that lenses are used to improve our vision is in this way.
  2. Magnifying glass is a prominent example of this type of lens in use as well. It creates an enlarged and vertical image of an object on the same side as the object itself if we place the object in front of it at a distance shorter than the focal length of the lens.
  3. Additionally, this lens is used to treat hypermetropia or long-sightedness. After that, we utilize this lens in cameras since it sharpens and clears the image by focusing light. Like this, we also discovered its use in compound lenses in various instruments, such as magnifying glasses. for instance, lenses for cameras, telescopes, and microscopes.
  4. Then you realize that while a basic version of these lenses may focus light into an image, the quality of the resulting image will be low. It will be better if we combine both lenses to fix the distortions and aberrations.

Functions of Convex Lens

We'll examine some of the purposes of convex lenses now: -

  1. First, this lens will create an image at focus that is inverted when the object is at infinity. Additionally, a picture develops between the focal point and the imaginary point when the item is beyond the latter. It is true, flipped, and weakened.
  2. Additionally, when an object is at a hypothetical location, an actual image, reversed, and the same size appears at the same hypothetical point.
  3. The image that forms beyond an imaginary point is actual, inverted, and magnified if the item lies between the focal point and the imaginary point.
  4. An image is at infinity and is real, inverted, and enlarged when the object is at the focus point.
  5. The picture that develops beyond the imaginary point and behind the object is virtual and amplified when the object is between the focus point and the center of curvature.

Facts about Convex Lens

  1. Because it causes light rays to converge, a convex lens is often referred to as a positive lens.
  2. A convex lens is typically defined as having an outward bulge that resembles a piece of a sphere.
  3. Convex lenses have narrower borders and thicker centers.
  4. The optical center, which is a point on the primary axis, is the center of a convex lens.
  5. A hypothetical line that passes via the optical center of the lens is the number one axis. 
  6. Transparent materials, such as glass or plastic, are used to make convex lenses. 
  7. A convex lens's refractive index is extra than 1, which denotes that it reduces the rate of light visiting via it. 
  8. One of the round surfaces of a convex lens is convex, and the other is concave. 
  9. A convex lens's power is expressed in diopters (D). The power is equal to the focal length in meters divided through itself. 
  10. Two focal points are present in convex lenses, one on every aspect. They are all equally spaced apart from the optical middle. 
  11. A convex lens's focal length (f) is calculated using the formula: f = 1 / (P), in which P is the lens's power, expressed in diopters.
  12. When the object is positioned beyond the focus point of the convex lens, a true, inverted image can be created.
  13. The ratio of the image height to the object height can be used to compute the magnification achieved by a convex lens.
  14. Convex lenses may focus parallel light beams at a particular location because they have a defined focal length.
  15. The focal length and strength of a convex lens increase with the degree of surface curvature.
  16. Chromatic aberration is a property of convex lenses that causes distinct hues of light to focus at marginally different locations.
  17. When seen through them, convex lenses can be used as straightforward magnifiers to increase the size of an object.
  18. The focal length shortens when a convex lens is submerged in water or any other liquid that has a greater refractive index than the lens.
  19. In telescopes and binoculars, convex lenses are frequently employed to collect and concentrate light for viewing.
  20. To create crisp and magnified images, convex lenses are also utilized in optical devices like microscopes and camera lenses.

What is Concave Lens?

A concave lens deviates a straight light beam away from the source and concentrates it into a warped vertical virtual image. It can be used to create both real and virtual images. At least one inner surface of concave lenses is convex. Because a concave lens is rounded in the center and curved outwards at the edges, a concave lens is also known as a diverging lens because it causes light to disperse. Because they make distant objects appear smaller than they are, they are used to correct nearsightedness.

The Formula of Concave Lens

The type and location of the image created by the concave lens are determined using the lens formula. The lens formula looks like this: -

1/f = 1/v+1/u

where v is the distance of the image from the center, u is the distance of the object from the center, and f is the focal length.

Uses of Concave Lens

  1. Telescopes: - In telescopes and binoculars, concave lenses are used to magnify objects. Concave lenses are inserted before or within the eyepiece of telescopes and binoculars because convex lenses blur and distort images, making it harder for users to focus.
  2. Eyeglasses: - Nearsightedness, or myopia, is most frequently treated with concave lenses. Myopia causes the eyeball to be overly lengthy, which causes images of distant objects to miss the retina. Concave lenses are therefore employed in spectacles to make up for the shortcoming by spreading out the light rays before they reach the eye. Thanks to this, a person can perceive distant objects more clearly.
  3. Peepholes: - Security tools like peepholes or door viewers provide a comprehensive view of everything beyond walls or doors. To reduce the size of the items and provide a wider view of the object or region, a concave lens is utilized.
  4. Lasers: - Laser beams are used in a variety of scanners, medical devices, and CD and DVD players. The apparatus functions properly because the laser beams, despite being extremely focused, are distributed. The laser beam is widened by small concave lenses, allowing it to access a particular location.
  5. Camera: - Combinations of convex and concave lenses are frequently employed by camera manufacturers to enhance the quality of images. Chromatic aberrations are distortions that appear in photographs when the camera's primary lens is only convex. Concave and convex lenses combine to eliminate unwanted effects.
  6. Flashlight: - Additionally, flashlights include concave lenses to enlarge the source's brightness. On the lens's hollow side, light rays fall, while on its other side, they split apart. This widens the beam of light by increasing the light source's radius.

Facts about Concave Lens

  • Shape: A transparent optical device with thicker borders and a concave lens that is thinner in the middle. On both sides, it features a curved surface.
  • A concave lens is also referred to as a diverging lens because it spreads out or diverges parallel incoming light beams.
  • The principal axis point on a concave lens principal axis where parallel light rays appear to diverge after passing through the lens is known as the focal point. The incoming parallel rays and the focus point are situated on the same side of the lens.
  • The distance between the lens's center and the focal point is known as the focal length of a concave lens. It is typically denoted by the letter "f." A concave lens' focal length is never positive.
  • A ray diagram can be used to visualize how light rays interact with a concave lens. Two rays are normally considered when producing a ray diagram for a concave lens: the parallel ray (which after refraction seems to come from the focal point) and the central ray (which passes through the center of the lens without deviating).
  • Concave lenses always provide shrunken, virtual, and upright pictures. On the same side as the object, the image is generated.
  • Magnification: A concave lens will never yield a magnification greater than 1, hence the image will always be smaller than the object.
  • Concave lenses are utilized in a variety of situations, such as:
    • Concave lenses are frequently used in corrective eyewear to diverge incoming light rays and correct myopia (nearsightedness).
    • Concave lenses are used in wide-angle lenses on cameras to widen the field of view.
    • Concave lenses are sometimes used in binoculars to provide a larger field of vision.
    • Projectors: To disperse the projected light and produce a broader image, projectors employ concave lenses.
  • Concave and convex lenses are frequently combined to construct more sophisticated optical devices, such as telescopes and compound microscopes.
  • Negative diopters (D) are used to quantify the concave lens's power. The power is the inverse of the focal length's absolute value in meters.
  • Concave lenses cause different hues of light to disperse or spread out, which leads to chromatic aberration.
  • Contact lenses: Some contact lenses with concave surfaces are used to treat eyesight issues.
  • Concave lenses can be utilized in safety goggles to increase field of vision and lessen distortion.
  • Virtual Image: A concave lens creates an image that can only be seen by the person gazing through the lens and cannot be projected onto a screen.
  • In a concave lens, the focal point is virtually placed on the same side as the subject but is inaccessible physically.
  • item Visibility: The picture is virtual, erect, and magnified when an item is placed between the concave lens and its focus point.
  • Concave lenses can be created using transparent materials such as glass, plastic, or other materials.
  • Spherical aberration is a condition in which light rays going through the edges of a concave lens concentrate at a different location than light rays passing through the center.
  • Concave lenses can be used to treat astigmatism in some circumstances by minimizing the disparity in focusing power between the various meridians of the eye.
  • A concave lens curves more sharply at the corners and less sharply in the middle.

Main Points of Difference Between Convex and Concave Lens

  1. Convex lenses are those that combine the light rays that pass through them at a certain spot. A concave lens scatters light rays that strike other lenses around.
  2. The curve of a convex lens faces outward, whereas a concave lens curve faces inward.
  3. The convex lens causes the light rays to converge and focus on a single point as they pass through it. The concave lens, on the other hand, causes the light rays to diverge, or spread out, as they pass through it.
  4. Convex lenses have a construction that is similar to having a thicker center and a thinner edge. Contrarily, the concave lenses have broader edges and thinner centers, in structure.
  5. A convex lens has a positive focal length, whereas a concave lens has a negative focal length.
  6. A convex lens often produces a real image, but when the item is in the focus and optical center, it can also produce a virtual image. On the other hand, the concave lens creates an image that is upright, virtual, and smaller than the object.
  7. Convex lenses' thicker centers make objects appear larger and closer. Contrarily, a concave lens makes an item appear closer and smaller due to its narrow center.
  8. For the treatment of farsightedness or hyperopia, convex lenses are employed. The concave lens, on the other hand, is effective in treating myopia or shortsightedness.


You may now have a clear knowledge of the differences between the two types of lenses after looking at the examples and statistics above. To create sharper, clearer, and superior images, convex and concave lenses are frequently utilized.


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"Difference Between Convex and Concave Lens." Diffzy.com, 2023. Sat. 02 Dec. 2023. <https://www.diffzy.com/article/difference-between-convex-and-concave-lens>.

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