Telescopes
Simple Prism
Bends lightSeparates colors
Prism Lens
Focal Point
Focal Length
Keplerian Refractor
ObjectiveLens
EyepieceLens
Typical small Refractor
Purpose of a Telescope
Gather lightSee fainter objectsProportional to the collecting area
MagnifyGreater detailM = focal length objective/focal length
eyepiece
ResolveSee objects close together
Light Gathering
Light Gathering
10.7 cm camera
15.2 cm camera
Resolution
Light Pollution
Problems with the Simple Refractor
white
Chromatic Aberration
Spherical Aberratio
n
Examples of Chromatic Aberration
Example of Spherical Aberration
Hevelius and his long telescope
Achromatic Doublet
Positive, crown glass
Negative, flint glass
40-inch Yerkes Refractor
Problems of Large Refractors
SupportCan only support lens by the edge
Absorption of starlightImperfections in the glass
Glass flows
Reflectors
Advantages of Reflectors
No chromatic aberrationNo spherical aberrationMirrors don’t have support
problemsNo problems with imperfections in
the mirror or absorption in the mirror
Problems of Reflectors
Early mirrors were metalTarnished easilyNot very reflective
Some light must be blockedUsually a second mirror is inserted to
divert light
Types of Reflectors
Newtonian Prime Focus
Cassegrain
Coudé
Earl of Rosse’s Leviathan
Mauna Kea
Keck Telescopes – 10 m
Large Binocular Telescope8.4 m each
Very Large TelescopeFour – 8 m
Giant Megellan Telescope24.5 m
The OWL Telescope(OverWhelming Large) – 100
m
Hubble Space Telescope
James Webb Telescope
The SFA Observatory
Cassegrain Telescopes
10-inch Schmidt-Cassegrain
8-inch Schmidt-Cassegrain
CCD Camera and Color Filters