Focal length of a Convex lens

The focal length of an optical system is the inverse of the system’s optical power; it measures how strongly the system converges or diverges light. A system with a positive focal length converges light, while one with a negative focal length diverges light. A system with a shorter focal length bends the rays more sharply, bringing them closer to the focus or diverging them faster.

A positive focal length is the distance across which collimated (parallel) rays are brought to a focus in the special situation of a thin lens in air, or a negative focal length specifies how far in front of the lens a point source must be positioned to generate a collimated beam. The focal length of a more general optical system has no intuitive meaning; it is merely the inverse of the optical power of the system.

Focal length

Longer focal length (lower optical power) leads to higher magnification and a narrower angle of view in most photography and all telescopes, where the subject is essentially infinitely far away; conversely, shorter focal length or higher optical power leads to lower magnification and a wider angle of view. In applications where magnification is done by getting the object close to the lens, such as microscopy, a shorter focal length (greater optical power) leads to higher magnification.

The focal length of a thin lens in air is the distance between the lens’s center and its principal foci (or focus points). The focal length of a converging lens (for example, a convex lens) is positive, and it is the distance at which a collimated light beam will be concentrated to a single spot. The focal length of a diverging lens (such as a concave lens) is negative, and it is the distance from which a collimated beam seems to be diverging after passing through the lens.

Let us consider the distance from the object to the lens is u, the distance of the lens to the image is v and the focal length f is related as:

1f=1u-1v

Focal Length of Convex Lens

The middle of convex lenses is thicker. Light rays passing through the lens are pushed closer together (they converge). A converging lens is one that is convex.

A thin convex lens’ focal length can be easily determined by projecting an image of a distant light source onto a screen. The lens is adjusted around on the screen until a sharp image appears. In this situation, 1 / u is insignificant, hence the focal length is given by

f∝v where v is image distance

When parallel light beams pass through a convex lens, the refracted rays converge at a single point, known as the principal focus. The focal length is the distance between the principal focus and the lens’s center.

The angle of view—how much of the scene will be captured—and the magnification—how large individual elements will be—are determined by the focal length of the lens. The smaller the angle of view and the higher the magnification, the longer the focal length. The wider the angle of view and the lower the magnification, the shorter the focal length.

Types of Convex Lens

There are basically three types of convex lenses:

Plano-convex Lens

The shape of this lens is Plano-convex.

On one side, it is curved outwards, while on the other, it is flat. The elements have a positive focal length and one spherical and one flat surface. These lenses are designed for applications that do not require a lot of parallel light. It’s used in a variety of applications, including pharmaceuticals, defense, and robots.

Double convex Lens

It bends outwards on both sides. Another term for it is the Biconvex lens, or just convex. It’s found in a variety of products, including projectors, monocular, telescopes, and cameras.

Concave-Convex Lens

It curls inwardly on one side while curving outwards on the other. It can be used to compensate for spherical aberrations in other lenses. Its job is to keep the laser beam under control. A concave-convex lens, often known as a meniscus, is a pair of lenses with one convex and one concave side.

Uses of convex lens

There are several uses of convex lenses in our surroundings. Some are listed below:

• Magnifying glasses
• Eye glasses
• Optical microscopes
• Projectors
• Cameras
• Human eye
• Telescopes
• Multi-junction Solar cells
• Peepholes in doors
• Binoculars

Conclusion 

In this article we have studied focal length of convex lenses and some other important terms. One of the most important characteristics of a lens is its focal length. It’s commonly expressed in millimeters by manufacturers (mm).

The distance between the rear principal point and the sensor is referred to as focal length, and it refers to the space between the lens’s center and the point where the light rays converge in the focal point.