Narrowband V coat. The coating has considerably reduced not only chromatic aberration bust also spherical aberration and coma aberration. These are designed with respect to three wavelength 480.0nm, 546.1nm and 643.8nm.
Beam splitter coatings are mainly used in precision optical systems, such as a rear projection, TV system, digital projection apparatus, digital camera, and CCD imaging detection system, to suppress infrared heat radiation interference that improves the optical quality.
Silver, aluminum, gold. There are also parabolic mirrors that are curved in only one direction and therefore focus light only in that direction (similar to cylindrical lenses).