Optical Telescope. Faint Light. Astronomical objects are distant and faint. Effectively at infinity Light collection is more important than magnification. Refraction Reflection. The Andromeda Galaxy (M31) subtends 3 ° . 6 times the moon
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Easy to calculate rays
Use Snell’s Law on a small part of a sphere.
Radius of curvature R
Focal length f
Index for air is 1Radius of Curvature
A circular hole produces rings around a central maximum.
84% of energy in centerAiry Disk
Yerkes 40 inch
Longer wavelengths - lower indexes
Blue light bends more than red
Compound lenses can compensate for chromatic aberration.Chromatic Aberration
Aspheric lenses can be used to correct the aberration .Spherical Aberration
A parabola for a focus at infinity
secondary diagonal mirror
Schmidt corrector lens
Observe at high altitude
Satellite telescopes avoid the atmosphere.
IRAS (1983) - first evidence of planets around other stars
Spitzer Space Telescope (2003-9).
Ultraviolet is largely absorbed by the atmosphere.
HST, GALEXInfrared and Ultraviolet
M81 from GALEX