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
No minimum for m = 0Fraunhofer Diffraction
A circular hole produces rings around a central maximum.
84% of energy in centerAiry Disk
The Rayleigh criterion is calculated from the first minimum of the Airy disk.
Aperture radius a
Bessel function J1Angular Resolution
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
Light that begins at one focus of an elliptical mirror converges at the other focus.
A parabola for a focus at infinity
secondary diagonal mirror
Schmidt corrector lens
REFRACTOR converges at the other focus.
Good for detail
Good for dim objects
Uniform treatment of colors
Combines best optical qualities
Good for photographyTelescope Advantages
Infrared is absorbed by water vapor. converges at the other focus.
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