Newtonian telescope secondary mirror. This design reduces the size and cost of the telescope with a shorter overall telescope tube length (with the corrector extending the focal length in a "telephoto" type layout) combined with a less costly spherical mirror. Commercially produced versions of this design have been noted to be optically compromised due to the difficulty of producing a correctly shaped sub-aperture corrector in a telescope targeted at the inexpensive end of the telescope market. Newtonian telescope The Newtonian telescope, also called the Newtonian reflector or just the Newtonian, is a type of reflecting telescope invented by the English scientist Sir
Newtonian gauge Newtonian gauge In general relativity, Newtonian gauge is a perturbed form of the Friedmann–Lemaître–Robertson–Walker line element. The gauge freedom of general relativity is used to eliminate two scalar degrees of freedom of the metric, so that it can be written as where the Latin indices "a" and "b" are summed over the "spatial" directions and formula_2 is the Kronecker delta. Conformal Newtonian gauge is the closely related gauge in which which is related by the simple transformation formula_4. These metrics are perturbed forms of the Friedmann–Lemaître–Robertson–Walker metric. They are called Newtonian gauge because formula_5 is the Newtonian gravitational potential of