University Optics 12.5mm guiding eyepiece
This 1986 University Optics guiding eyepiece has a reticule with etched dual line cross hairs. The lines are 0.2mm apart (200 microns) The spacing viewed against the sky depends on the telescope properties. Astronomers use these eyepieces by manually keeping a guide star in the central box. This allows a camera attached to the telescope to accumulate an image without the subject trailing. Normally a small adjustable LED light source is fitted to the mount seen here on the right side. It is powered by small button cells. Then the cross hairs can be seen glowing softly.