lecture 4: Telescopes
The Basic setup of a telescopes
build to observe parallel waves.
two principles
reflection
refraction and lens' image
six kinds of structure
singlets: Prime focus
doublelets:Newtonian, Cassegrain, Gregorian
triplets: Schmidt-Cassegrain, Schmidt Camera
4 kinds of Focus
Primary focus
Cassegrain focus
Nasmyth focus
Coude focus
2 kinds of mounts
equatorial/polar
Alt-az
dome/building
How good is the image?
Aberrations: the image isn't a copy of the source
on-axis:chromatic, spherical
off-axis: coma, astigmatism,distortion, field curvature, vignetting
how large is the image?
plate scale
how bright/fast is the image?
limiting magnitude
focal ratio
how wide can we see?
Field of View
the limitation of finess:diffraction and Airy disk
Adaptive Optics helps
other kind of electromagnetic wave might help
infrared or lower frequency: black hole
ultraviolet or higher frequency:Einstein Probe
Signal-to-Noise Ratio
the essense of make a detection