What optical device is used to magnify or reduce an image?

A lens is an optical device specifically designed to bend and focus light rays, enabling it to magnify or reduce the size of an image based on its shape and curvature. When light passes through a lens, it can diverge or converge, allowing for the magnification of small objects when using a convex lens, or the reduction of images when a concave lens is used. The capability to alter the image size is essential in various applications such as cameras, microscopes, and glasses.

Conversely, mirrors reflect light to form images but do not inherently magnify or reduce them. Prisms can disperse light into its constituent colors but do not serve the primary function of magnifying or reducing images. Filters allow certain wavelengths of light to pass while blocking others, but they do not manipulate the size of the images produced. Therefore, the defining function of a lens is what makes it the correct answer for this question.