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