1. 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.

2. 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 size Primary mirror: 2.4 m (94.5 inches) in diameter Secondary mirror: 0.3 m (12 inches) in diameter Angular resolution Hubble'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.

4. 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

6. Multiple lens correction – expense and more absorption of light

8. Catadioptric Telescope

10. 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

16. Cheap Telescope design – the Dobsonian Telescope Newtonian Reflector

17. Basics Magnification M = fofo fefe f o = focal length of the objective f e = 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

18. Basics Resolution  min = 1.22  D Put in definitions, do calc of angular diameter minimums for various wavelengths