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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

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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