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Introduction to Optical
Telescopes
Mel Blake
PARI SSL 2006
Purpose of Telescopes
1. Collect light from faint objects
2. Resolve objects that are near each other
3. Magnify the view of an object
2
Optical Telescopes
• Reflectors
• Refractors
3
Optics
• Lens – directs light by bending of light into
media of differing densities
• Focus – point at which light is directed
• Focal plane – two-D area where image is
formed
• Field of view – area on the sky images
cover
4
Refractors
• Use the bending of
light entering denser
media to direct light to
a focus
• Largest is the 100inch
Yerkes refractor
5
Reflectors
• Two main types
– Newtonian telescope
– Cassegrain telescope
• Light can be redirected with other optics
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Newtonian Telescope
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Cassegrain Telescope
8
Advantages of refractors
• Superior image quality if optics are welldesigned
• Chromatic aberration deteriorates images if
poorly constructed
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Reflectors Advantages
• Need to figure and polish only one surface
• Mirror is at the bottom so structurally more
stable
• No chromatic aberration
• Reflectors are shorter for the same aperture
so construction costs are lower
10
Telescope Mounts
• Alt-Az mounts (altitude azimuth)
• Equatorial (lined up with north, celestial
equator)
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Video
• Gemini Virtual Tour
– What kind of telescope is it?
– What sort of detectors?
– What sort of mount?
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