A convex lens is a simple, curved lens that causes rays of light from a subject to converge at a focal point, forming a sharp image. Convex lenses are widely used in cameras, enlargers, magnifying glasses, and optical instruments to focus light and control image clarity. In photography, they play a crucial role in creating well-defined, properly focused images and can affect perspective, depth of field, and magnification depending on their curvature and focal length.