A lens is an optical instrument that deviates the coming light rays from a different medium when they pass through the lens. This is due to the refraction of light.
Convex lenses are converging lenses.
Convex lenses are frequently used in cameras to both foci and enlarge an image.
Convex lens are used in photographic cameras so that real images formed can be taken on-screen as a concave mirror does not form a real image.