Convex Lens:

You can purchase a convex lens in nearly any novelty store or department store. In a fine hobby store you must be able to find a "magnifying glass" up to 10 cm or even 15 cm in diameter. The word convex occurs from the fact that one or both faces of the glass bulge outward at the center. The convex lens is at times termed as a converging lens. It fetches parallel light rays to a sharp focus or focal point, as shown in figure below, whenever those rays are parallel to the axis of the lens. It can also collimate (i.e., make parallel) the light from a point source, as shown in the next figure below.

Figure: (a) A convex lens focuses parallel light rays to a point. (b) The similar lens collimates light from a point source at the focus.

The properties of a convex lens based on the diameter and the difference in thickness among the edges and the center. The larger the diameter is, the greater is the light-gathering power. The bigger the difference in thickness among the center and the edges, the shorter is the distance among the lens and the point at which it fetches parallel light rays to a focus. The effective region of the lens, measured in a plane perpendicular to the axis, is termed as the light-gathering region. The distance among the center of the lens and the focal point (as shown in figure above) is termed as the focal length. When you look via a convex lens at a close-up object like a coin, the features are magnified; they emerge larger than they look with the unaided eye. The light rays from an object at a large distance from a convex lens converge to form an actual image at the focal point.

The surfaces of nearly all convex lenses are spherical. This means that when you could find a large ball containing just the correct diameter, the curve of the lens face would fit neatly within the ball. Some of the convex lenses have similar radius of curvature on each face; others have dissimilar radii of curvature on their two faces. Some of the converging lenses contain one flat face; these are termed as plano-convex lenses.