The German word for "single",  einzel   (YNE-tzell) , names a type of one of these devices composed of three cylinders, of which the first and third are held at the same potential.
The German word for "single",  einzel   (YNE-tzell) , names a type of one of these devices composed of three cylinders, of which the first and third are held at the same potential. In one theory, these objects effectively take the Fourier transform of a plane wave and map it as a point spread function onto a backplane. An effect named for these devices can form Einstein rings; that effect can be used to map (*) exoplanets. The power of these objects is measured in inverse-meters or diopters, and depends on the reciprocal of two radii, according to an equation named for a "maker" of these things. These devices can produce comas. When rays traced through them do not convene at a single point, they give spherical aberrations. For 10 points, name these devices that refract and focus light.
The German word for "single",  einzel   (YNE-tzell) , names a type of one of these devices composed of three cylinders, of which the first and third are held at the same potential.
 lens es [or electrostatic  lens es; or einzel  lens es; or gravitational  lens es] 