Reflecting telescope manageable at large focal ratios — most Schiefspieglers use f/15 or longer, which tends to restrict useful observation to the moon and planets. A number of variations are common, with varying numbers of mirrors of different types. The Kutter (named after its inventor Anton Kutter) style uses a single concave primary, a convex secondary and a plano-convex lens between the secondary mirror and the focal plane, when needed (this is the case of the "catadioptric Schiefspiegler"). One variation of a multi-schiefspiegler uses a concave primary, convex secondary and a parabolic tertiary. One of the interesting aspects of some Schiefspieglers is
Parallel projection has the following properties. Orthographic projection is derived from the principles of descriptive geometry, and is a type of parallel projection where the projection rays are perpendicular to the projection plane. It is the projection type of choice for working drawings. The term "orthographic" is sometimes reserved specifically for depictions of objects where the principal axes or planes of the object are parallel with the projection plane (or the paper on which the orthographic or parallel projection is drawn). However, the term multiview projection is also used. In "multiview projections", up to six pictures of an object are produced, with