Cassegrain Nasmyth
The Cassegrain Nasmyth telescope has the same optical design as the classical Cassegrain telescope except for a small tertiary mirror which sends out the light on the side of the telescope tube instead of through a hole in the primary mirror. This design is common in large telescopes, e.g., the W. M. Keck Observatory. Figure 1 shows the light-path from a star based on the 0.61m telescope in Oslo. Figures 2 and 3 show the use of a focal reducer, flip mirror unit, ocular and CCD camera. See alNasmyth telescope, so: Nasmyth telescope. References

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Telescope Built For Visual Work
A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, the word ''telescope'' now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors. The first known practical telescopes were refracting telescopes with glass lenses and were invented in the Netherlands at the beginning of the 17th century. They were used for both terrestrial applications and astronomy. The reflecting telescope, which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope. In the 20th century, many new types of telescopes were invented, including radio telescopes in the 1930s and infrared telesc ...
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