The Nasmyth telescope, also called Nasmyth-Cassegrain, is a reflecting telescope

Reflecting telescope

A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...

 developed by James Nasmyth

James Nasmyth

James Hall Nasmyth was a Scottish engineer and inventor famous for his development of the steam hammer. He was the co-founder of Nasmyth, Gaskell and Company manufacturers of machine tools...

. It is a modified form of a Cassegrain telescope, mounted on an alt-azimuth mount.

Scheme

As in the Cassegrain telescope, the light falls on a concave primary mirror, then goes into a convex secondary mirror. However there is no hole in the primary mirror. Instead a small flat mirror reflects the light to one of the sides of the telescope. This flat mirror is placed on the altitude axis, so that the exit beam comes out of a hole in the middle of the altitude bearing. This means the eyepiece or instrument does not need to move up and down with the telescope; therefore a heavy instrument can be used without upsetting the balance of the telescope or increasing the load on the altitude bearings. This has significant advantages for spectrographs and other heavy instruments typically used at research observatories. Most modern research telescopes can be configured into a Nasmyth telescope (i.e. to use the "Nasmyth Focus").

Observatories

The Sierra Nevada Observatory

Sierra Nevada Observatory

The Observatorio de Sierra Nevada is located at Loma de Dilar in the Sierra Nevada mountain range, in the province of Granada, established in 1981...

(OSN) in Spain has 2 Nasmyth telescopes, including a 1.5 meter diameter aperture one.

External links

• Nasmyth Telescope, Murdin, P., Encyclopedia of Astronomy and Astrophysics