Abstract: A testing apparatus for an optical system comprises a plurality of markers disposed along an axis to be aligned with the optical axis of the optical system, the markers being axially spaced from one another and angularly displaced relative to one another so as to effectively define a helix about the axis. When viewed from one end of the apparatus the markers provide focusing and depth of field information, and some aberrational information about the optical system. Preferably the markers are spaced so as to correspond to the depth of field of the lens aperture stop values of a camera, allowing the aperture settings of the camera to be tested.