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