Which instrument is used for magnifying the edge of a rigid contact lens?

The instrument specifically designed for magnifying the edges of a rigid contact lens is the shadowgraph. This device works by utilizing a focused light source to project an image of the lens onto a screen or surface, allowing the user to analyze the edge contours and any surface imperfections. By magnifying the lens' edges, the shadowgraph aids in evaluating how the lens sits on the eye and helps in determining proper fit and comfort for the wearer.

In contrast, the other options mentioned serve different purposes. A measuring magnifier is generally used for enlarging text or small objects and is not tailored for optical evaluations of lenses. A radiuscope primarily measures the radius of curvature of a contact lens, which does not inherently involve edge magnification. Meanwhile, a contact lens fitting set is a collection of various trial lenses used to assess fit and comfort rather than a tool for detailed magnification of lens edges.