By considering how these objects Fourier transform an input into a point-spread function on the back plane, they can be shown to act as low-pass filters. The formula (read slowly) “n minus 1 times a difference of inverse radii”gives the (-5[1])“power” of these objects in an equation named for a “maker” of these (10[1])objects. The power of these objects is measured (10[1])in (10[2])diopters. Thin examples of these objects are governed by an equation stating that (read slowly) “one over the object distance plus one over the image distance is equal to one over (10[1])the focal length.” Like mirrors, parabolic examples of these objects do not have spherical aberration. For 10 points, name these objects that refract and focus light. ■END■