Basic Telescope Design Refractors: Utilizes a lens (or lenses) to produce the refraction of light to...
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Transcript of Basic Telescope Design Refractors: Utilizes a lens (or lenses) to produce the refraction of light to...
Basic Telescope Design
Refractors: Utilizes a lens (or lenses) to produce the refraction of light to focus light from an object. The main lens is called the objective.
The image is then examined with a single lens called a magnifier.
Reflectors: Utilizes a mirror to produce reflection of light to focus light from an object.
The image is then examined with a single lens called a magnifier.
Hubble works on the same principle as the first reflecting telescope built in the 1600s by Isaac Newton. Light enters the telescope and strikes a concave primary mirror, which acts like a lens to focus the light. The bigger the mirror, the better the image.
In Hubble, light from the primary mirror is reflected to a smaller secondary mirror in front of the primary mirror, then back through a hole in the primary to instruments clustered behind the focal plane (where the image is in focus). Mirror sizePrimary mirror: 2.4 m(94.5 inches) in diameterSecondary mirror: 0.3 m(12 inches) in diameter Angular resolutionHubble's angular resolution is 0.05 arcsecond. This is the "sharpness" of Hubble's vision. If you could see as well as Hubble, you could stand in New York City and distinguish two fireflies, 1 m (3.3 feet) apart, in San Francisco.
Advantages:
All of the light collected has a direct path to the eyepiece
Disadvantage:
Size – length of the tube must match the length of the objective
It is hard to make large lenses
Some light is absorbed by the lens material
Chromatic aberrations
Spherical aberrations
Multiple lens correction – expense and more absorption of light
Catadioptric Telescope
Advantages
Cheap to make
Can make large mirrors with precision
Folded construction – length of the scope does not need to equal the focal length of the objective
Disadvantages
Must have obstructions in the light path to get light to the eyepiece
Spherical aberrations
Cheap Telescope design – the Dobsonian Telescope
Newtonian Reflector
Basics
Magnification
M = fo
fe
fo = focal length of the objective
fe = focal length of the eyepiece
High magnification requires either a long focal length objective or a short focal length eyepiece (or both)
Long focal length optics is fairly easy to make, well designed short focal lengths are harder to produce
Basics
Resolution
min = 1.22
D
Put in definitions, do calc of angular diameter minimums for various wavelengths