Working Mechanism of Concave Lenses as a Reflector in a Projector

A concave lens is one of the most vital components of a projector. It works in tandem with light particles by focusing and reflecting them off the surface. The reflection is able to project and display an image or video.

Technically speaking, the concave lens can bend light rays into a single focal point. This is the same principle as to how all sorts of lenses work. A concave lens works by “bending” light coming from both sides to a common focal point, the center of curvature. If the lens were not bent, its focal point would be at infinity. In a projector, the projection lens (or exit lens) is used to display an image on a screen. It does this by focusing the light passing through it onto the screen. The curvature of the concave lens can be referred to as a parabola, hence the following name, parabola-mirror (or mirror and parabola).

Any given projector needs to use concave lenses. If a low-quality concave lens is used instead of a higher quality one, image degradation may occur. This degradation will lead to poor focus and the occurrence of a cone-shaped hotspot, leading to a poor quality image. This will also reduce the life of the lamp because as the light from the lamp reaches a concave lens, it will diverge and come in contact with the lamp’s surface. If there is divergence, it will heat up and shorten the life of a lamp.

Why Do We Need Concave Lenses In Projectors? 

Since a projector is used to project an image on an opposite surface, it is important for the surface to be large enough. The larger the screen, the better quality of the image can be projected. If there were no reflections from surfaces, it would mean images being projected would meet the eye directly; they will not appear larger than the size of the picture in reality. At this point, manufacturers began making concave lenses that will assist in projecting images onto large surfaces. “Parabolic mirrors” were first used in projectors but were later replaced by the “concave lens.”

Concave lenses are widely used in projectors because they allow images to be projected at a distance without losing quality. It also allows the images to be viewed at a larger screen compared to other lenses such as spherical mirrors. Although spherical mirrors require walls and ceilings to make images reach far distances, concave lenses work differently. 

Demonstration On How A Concave Lens Works 

Assume that we have a projector placed on the other side of a screen and an object (a toy car) placed at a distance from it. If we place a concave lens in front of the toy car, rays will come out from both sides of the concave lens, which, from our viewpoint appear to be parallel. Now, if we move the lens closer to the screen, rays will also come close to each other. Ultimately, the projection will come closer too.

Now, let us go back to the toy car. If we do not place a concave lens in front of it, then only one ray is required to reach the screen. However, if we want rays from both sides of the concave lens to reach the screen, then we need multiple rays which must be parallel in direction. This can be achieved only by using a concave lens.

Type of Lenses in a Projector and Their Functions

There are three types of lenses available in a projector. In the front of the lamp or light source, a Fresnel lens is provided for collimating the light. This lens collects the rays coming from the lamp and focuses them. Next in line is the multi-lens, which helps in forming an image on the screen. The final component is the concave lens which works as a reflector by reflecting light off its surface.

What Are Concave Lenses Made Up Of? 

Concave lenses are made from glass. They are available in a wide variety of sizes which are purchased depending on the screen size. Lenses with high curvature are more beneficial as they will reflect much more light and can be placed close to the screen. However, if there is too much distance between the screen and the lens, then images may appear dimmer than they actually are.

Image Quality and Concave Lenses 

It is important to maintain quality images in a projector, especially when it comes to watching television. This is because everyone is used to see high-quality pictures, but tend to get disappointed when the image quality is not adequate. Manufacturers of projectors need to make sure that image quality does not degrade over time. This can be achieved by installing high-quality lenses that provide bright images and maintain good focus. 

Concave lenses transmit a large amount of light, up to 70%, compared to spherical mirrors. Because of the large amount of light it transmits, concave lenses require fewer layers than spherical mirrors and, therefore, can produce brighter images. Technically speaking, concave lenses have been known to project images with an impressive contrast ratio of over 1000:1 in an LCD projector.

Degradation of Image Quality – What Is Its Solution?

To avoid degradation in image quality, a high-quality concave lens should be used to ensure the exact angle of reflection. The angle of reflection can vary significantly from one concave lens to another. So it’s vital to ensure that you use a high-quality one. Also, this type of lens has better thermal conductivity than others, which helps cool the lamp conveniently and keeps the projector safe from any damage.

Problems Occurring While Using Low-Quality Lenses

1. Performance can deteriorate over time.

2. The lamp will heat up in quick time with the use of low-quality lenses. 

3. Concave lens will also reduce the life of the lamp due to increased heat. 

4. Projector will work for short periods of time with poor focus and a cone-shaped hotspot.

5. The projector will get stuck frequently and will incur high maintenance costs. 

Hey! Do You Wanna Buy Best Projector For Gaming Then Click Me.


Concave lenses play an important role in providing sharp and bright images. If you are using projectors to watch television, then it is recommended that you use a concave lens. It will ensure images are crisp and clear, even if you have a large screen. Also, these lenses are available in different shapes and sizes, so you can easily buy one that is suitable for your projector. 

Hope this article was informational and provided you with the relevant data about concave lenses and their working.


Q. When should a concave lens be used for a projector? 

A. Concave lenses should be used, as shown in this article. However, if you are sure about the manufacturer of the concave lens, then it is recommended to use that one. If you’re using a projector that uses a concave lens of different make for each projector and if these concave lenses have different dimensions, it wouldn’t be wise to use the same lens even if when you do this, the image quality will not degrade.

Q. What should be considered when buying a concave lens for a projector?

A. Always buy lenses that are of good quality. Also, try to ensure that there is no degradation in image quality because of using a different type of concave lens.

Q. Does concave lenses used in a projector matter? 

A. Yes, as concave lenses are devices used in a projector, they are essential to use high-quality ones.

Q. What are large concave lenses used in projectors? 

A. A large concave lens is kept at the front of a projector as it helps deliver a proper image to the audience. 

Q. What is the difference between a conic lens and a concave lens? 

A. Conic lenses are made up of glass whereas concave lenses are made out of plastics. Large concave lenses provide more light that results in brighter images compared to conic lenses. 

Q. Are concave lenses used in cameras?

A. Yes, they are. Convex and concave lenses are used in cameras depending on the requirement of the camera functionality.