about RC telescope

edwintcf

據我所知RC 鏡用左兩塊hyperbolic mirror, 並冇glass的,
所謂既hyperbolic mirror 同concave mirror 有咩分別?

Wales

拋物面鏡、球面鏡、雙曲面鏡(hyperbolic mirror)等都可以是凹面鏡(concave mirror)。

mca

傳統的 Cassegrain 在寬視場時往往彗差 (coma) 和 球面像差 (spherical aberration) 過大， RC 設計便將反射主鏡和副鏡磨制成 雙曲面形  (hyperbolic) 來改善缺點，2.4 米的哈勃太空望遠鏡、 1990 年代的 10 米 Keck Telescope (共兩座) 、2000 年代的 8 米 Very Large Telescope (共四座) 的基本設計是 RC。

參考  http://en.wikipedia.org/wiki/Ritchey-Chr%C3%A9tien_telescope

Alan Chu

edwintcf

it is the hyperbolic mirror that i dont understand it's principle.
for example how would be the light diagram if a beam of light is projected onto the mirror?
thx!

mca

Hi Edwin,

The light path in a RC-telescope is simply same as a classical Cassegrain telescope, their only differences are the mirror curvatures and their separations. In practice, a set of equations (the so called "Schwartzchild’s equations") are given to the RC system designers. You can find these equations in Chapter 21 of the popular book “Telescope Optics” by Rutten & van Venrooij. Basically there are 2 equations for RC telescopes. By setting two parameters (“A“ &“B”) in the equations to zero, the coma and spherical aberration are theoretically eliminated and thus we have a RC.

For simple introduction without going to the design equations, you may refer to

A Cassegrain Primer
http://www.rfroyce.com/cassegrains.htm
(The author is R F. Royce. He also produces excellent mirrors by handcraft, and I am in fact one of his customers.)

Basics for Conics, please read HYPERBOLA Section)
http://www.mathacademy.com/pr/prime/articles/conics/index.asp

X-ray optics
http://www.x-ray-optics.de/index ... emid=71&lang=en

http://www.mathreference.com/la-qf,hypmir.html


Hope above helps as I am not a mirror professional.

Alan Chu