The word ‘lens’ has been derived from the Latin word ‘lentil’ bean that was in the shape of a Bi-convex lens. It’s the shape of the lens that causes light rays to bend out in specific directions and ways as it passes through the lens itself whether it’s concave or convex. A convex lens is also called a converging lens as it converges the parallel light rays towards a single point on the opposite sides of the lens. Whereas, a diverging or also called concave lens diverges parallel rays to the optical axis. It’s the difference in the index of refraction
As per the refraction rule, parallel rays travel towards the principal axis of the plan-convex lens and refracts light through the lens, and travel via the focal point on the opposite of the lens. Whereas, in diverging lens parallel rays travel towards the principal axis of the plano-concave lens that refracts via the lens and travels in a line with the focal point.
Types of Spherical Lens
- The biconvex lens: It is the best option when your image and the object are at an equal distance from the lens that creates a magnified image of ratio 1:1. The symmetry of this lens reduces with spherical aberration and chromatic aberration and it’s the same radius of curvature that reduces in the spherical aberration too. These are converging or positive lens, curvature on both sides of the lens, the focal length is defined positive, it’s thicker at the center than towards the edges, there are two focal points that form a real and virtual image.
- Plano Convex lens: It is the best for collecting and collimating light. The focus should always be on the rays of light towards a single focal point. When the image and object are located at a variety of distances from the lens, the asymmetry of the plano-convex lens decreases with spherical aberration. These lenses are used the best when such objects are placed at infinity and the image is at a focusing point. It’s always recommended to place out the curved surface in a way that it faces the largest object distance and reduces the spherical aberration. The best usage of this lens is when it’s recommended to place towards the curved surface facing the largest object at a distance. It’s a positive or converging lens with curvature on one side of the lens, thicker at the center, the focal length is positive, it has only one focal point that forms a real and virtual image.
- Biconcave lens: It is one of the most amazing options when the image and the object are at an infinite conjugate with the ratio of 1:1 and a converging input beam. The output beam diverges from the virtual image and the focal length lies between the lens and the virtual image. The curvature is on both sides of the lens, these are also called a diverging lens, they are thinner at the center, the focal length is negative and there are two focal points. It forms a virtual image that’s tinier than the object itself.
- Plano Concave lens: It is diverging lenses with curvature on one side of the lens, thinner at the center, focal length-negative, and has one focal point. It balances the aberration with other systems equally well.