1. A Basic Refractor Telescope The size of the telescope is the diameter of the light-collecting lens

3. “Normal” Eye Refractive Errors FarsightednessNearsightedness

4. Limitations of Refractors Lens must be made of high-quality glass with no imperfections Larger lenses weigh a lot; lenses can be supported only around their rims The lens will sag under its own weight So, the largest refractor telescope anyone has built is about 1.1 m.

5. A Basic Reflector Telescope The size of the telescope is the diameter of the objective mirror

7. Usefulness of Reflectors Objective (mirror) can be made of many things, even plastic or metal Only one side of the mirror is polished Mirror can be supported from its entire back, not the rim only So, all large modern telescopes are reflectors because they are easier to make and maintain.

8. A Prime Focus Reflector (some light blocked)

9. A Newtonian Reflector (secondary mirror)

10. A Cassegrain Reflector (hole in primary mirror) Example: Hubble Space Telescope

11. Resolution vs. Magnification RESOLUTION: a telescope’s ability to distinguish fine details in an image. MAGNIFICATION: focal length of objective focal length of eyepiece So, magnification depends on the eyepiece used in the telescope.

12. Hubble Space Telescope