PX158 - E1 - introduction

the light gathering power is proportional to the collecting area of the telescope (aperture)
human eye pupil, $d \approx 5 m m$
giant squid pupil, $d \approx 90 m m$
difference in light gathering power:

Δ = \frac{π r_{s q u i d}^{2}}{π r_{h u m a n}^{2}} \approx 18^{2} = 324

types of telescopes

refracting telescope

the lens is hard to make perfectly, and imperfections cause image distortions
also difficult to make a lens that works over a wide wavelength range

reflecting telescope

a parabolic mirror design is needed, which can be produced more easily and larger than lenses

combination

the large mirror can be spherical, which is much easier to produce

cameras

using small angle approximation:

α = \frac{l}{f}