Download Reflecting Telescopes

Reflecting Telescopes
Mirrors
• A flat mirror reflects light in straight lines.
• A curved mirror can focus light to a point.
• A perfect parabolic mirror has a focal length like a lens.
– All frequencies focused to the same point
focal length
focal point
Newtonian Reflector
• A primary mirror and eyepiece are combined.
• The telescope is cheaper, because a mirror is easier to
make than a lens.
secondary diagonal mirror
primary mirror
eyepiece
Schmidt-Cassegrain Reflector
• Cassegrain focus makes the tube up to three times longer.
• The extra mirror can distort the image.
• Schmidt corrector lens corrects for this distortion, called
spherical aberration.
Schmidt corrector lens
eyepiece
Telescope Advantages
•
•
•
•
REFRACTOR
Superb resolution
Good for detail
Rugged alignment
Transports well
•
•
•
•
REFLECTOR
Inexpensive optics
Large aperture
Good for dim objects
Uniform treatment of colors
SCHMIDT-CASSEGRAIN
• Portable size
• Combines best optical qualities
• Good for photography
Altazimuth Mount
• Telescope mounts should permit two directions of motion.
• Altazimuth mounts directly control altitude and azimuth.
altitude control
azimuth control
Equatorial Mount
• Altazimuth mounts do not track with the star’s movement.
• Equatorial mounts are oriented to the pole.
• Allows control of declination and right ascension.
declination axis
polar axis
Keck Reflector
•
•
•
•
World’s largest reflector is in Hawaii.
400 inch aperture, f/1.75.
Focal length is 57.4 feet.
Telescope height is 81 feet.
Keck Observatory