Application: IV. Telescopes
The idea is again to increase the angle through which we observe a distant object: impression of getting it closer
Done by using converging lenses--> refracting telescopes
magnification of the telescope: ratio of the focal lengths of the objective and eyepiece
to get big magnification: long telescopes
as magnification increases the brightness decreases
to get big brightness --> big objective lens, BUT: but big lens --> big aberrations
good telescopes: expensive! Cheaper possibility to use big curved mirror (no chromatic aberration)--> reflecting telescopes