Siemens star

A Siemens star, or spoke target, is a device used to test the resolution of optical instruments, printers, and displays.

It consists of a pattern of bright "spokes" on a dark background that radiate from a common center and become wider as they get further from it.

When printed or displayed on a device with limited resolution, however, the spokes touch at some distance from the center.

Siemens stars are similar to the sunburst pattern used as a background in graphic design, as in the Japanese Naval Ensign, Russian Air Force flag and Jordanian Royal Standard.

(Spurious resolution appears similar to aliasing, but it is a purely optical phenomenon, so it occurs without need of pixels.)

A Siemens star
A Siemens star with gradually increasing defocus error shows increasing spurious resolution.
A Siemens star with defocus error shows spurious resolution, in the form of alternating bands.
A Siemens chart filter in a collimator , used for auto-focus calibration of digital still cameras
A Siemens star with 128 spokes. It shows aliasing in the center, where the spokes are smaller than the pixel pitch. (It is not blurred or aberrated, so it does not show spurious resolution.)