A reflecting telescope that incorporates two spheroidal concave mirrors. The secondary mirror is offset from the primary, and brings light to a focus adjacent to the primary. This gives an all-reflecting system without the central obstruction usually caused by the secondary. However, the focal ratio of the system is high, giving a high magnification and limited field of view. Aberrations limit the aperture to about 100 mm. A variant, called a trischiefspiegler, includes a third mirror, which allows the design to be used for larger apertures. The name derives from the German for ‘tilted mirror’.