1. Chapter 5 Telescopes: Refracting , Reflecting, Cassegrain.
Resolution, LGP, resolving power.
Aberration
magnification
Photometers, Spectrometers (Spectroscopes)
Radio telescopes, detectors & interferometry.

2. Telescopes: Parts of a telescope
Uses a mirror to bend light to a focus.
Uses a lens to focus light.
Telescopes: Parts of a telescope

3. Telescopes: Cassegrain design

4. Telescopes: Function & Problem
LGP (Light gathering Power) The amount of light a telescope can gather, dependent on size of lens/mirror ( aperture diameter).
Resolving Power (angular resolution) – ability of a telescope to form separate, distinct images of objects lying close together in a field of view.
Chromatic Aberration: Occurs when a lens bends higher frequency components of visible light more than the lower frequency components. The result is a colored halo around the image. Fig. 5.5, page 111.

5. Telescopes: lenses vs. mirrors
Lenses tend to focus the component frequencies of white light differently, bluer ( high energy) light bends more readily than red (less energy) light, [Chromatic Aberration effect]. Mirrors don’t have this problem.
Absorption is a problem for high energy ( IR, UV) radiation traveling through a lens. Does not affect mirrors.
Large lenses are quite heavy in contrast to mirrors which can be supported over their back surfaces.
A lens has to be carefully polished on 2 surfaces, a mirror has only one surface.

6. Telescopes: Cassegrain design.
In large Reflecting telescopes, the tube length can be quite long. The Cassegrain design overcomes this problem because the extra light path allows for a shorter tube.
The Coma effect: When not all light is focused properly to a fine point. The Cassegrain design allows for a correcting lens (plate) to correct this effect by bending the incoming light.
Incoming starlight
Primary mirror
Correcting lens

7. fe – eyepiece focal length
Magnification
M = f0/fe
Where f0 – objective focal length
fe – eyepiece focal length fe f0