Telescope Objective and Eyepiece望远镜的物镜与目镜.ppt

Telescope Objective and Eyepiece望远镜的物镜与目镜
Telescopes – Mirrors and Lenses
Telescopes are basically a large mirror (reflecting) or a lens (refracting)
Consider the human eye as ‘telescope’
What determines the “power” of a telescope ?
Collecting Area
Lens
Retina
Eye could be a “refracting” telescope,
but the size is very small
Collecting Area = Power
A = p ( d / 2)2 ; d – diameter
Diameter of the telescope indicates its power
Largest optical telescope: Keck 1 and 2, each with a mirror of 10 m diameter
Large Binocular Telescope (LBT): Ohio State, Arizona, Germany, Italy  Two 8.4 m mirrors in a binocular shaped mount
HST – Only 2.4 m, but with a huge advantage
How much more powerful than HST is the Keck (neglecting that advantage) ?
New 30m telescope on the drawing board
Large Binocular TelescopeMount Graham, Arizona
Objective and eyepiece
Telescope  Objective and Eyepiece
The main function of a telescope is to collect as much light as possible from the source, NOT to magnify an image
Need bigger and bigger telescopes!
The main mirror or lens of a telescope is called the OBJECTIVE
The Eye-Piece (small lens or mirror) is to magnify the image after it is formed from the light collected by the objective
Properties of Light and Telescopes
Reflection  Mirrors
Refraction  Lenses
Refractive Index
Speed of light slows down in a medium !
The ratio of the speed of light in vacuum to the speed in a medium
c / v = m
‘mu’ is called the Refractive Index
Material R.I.
Water 1.33
Glass 2.6
Bending of light (diffraction) depends on R.I of the medium and wavelength of light l