lecture 4: telescopes

telescope basics

assumptions

parallel rays of light

stars are point sources

focus

primary focus

cassegrain focus

nasmyth focus

coude focus

telescope mounts

equatorial/polar

alt-az

abberations

spherical aberration: on-axis aberration

focal length & focal plane

coma: off-axis aberration

astigmatism

distortion

field curvature

vignetting

chromatic aberration

quantifying the performance

plate scale: S = Fθ

focal ratio

R = F/D

measures how quick can we get light

fast optics: small f/R

field of view

point spread function(PSF)

describe how the telescope responds to a point source

diffraction

airy disk:θ = 1.22λ/d

reyleigh criterion: resolution limit = θ

seeing

adaptive optics(AO)

SNR

signal to noise ratio

longer exposure time -> higher SNR