5. Image from http://commons.wikimedia.org/wiki/File:Refraction.PNGhttp://commons.wikimedia.org/wiki/File:Refraction.PNG

13. Image from http://en.wikipedia.org/wiki/File:Lens-coma.svghttp://en.wikipedia.org/wiki/File:Lens-coma.svg

14. Image from http://en.wikipedia.org/wiki/File:Gregory-Teleskop.svghttp://en.wikipedia.org/wiki/File:Gregory-Teleskop.svg

15. Image from http://en.wikipedia.org/wiki/File:Newton-Teleskop.svghttp://en.wikipedia.org/wiki/File:Newton-Teleskop.svg

17. Image from http://en.wikipedia.org/wiki/File:Schema_lame_de_Schmidt.svghttp://en.wikipedia.org/wiki/File:Schema_lame_de_Schmidt.svg

19. Image from http://en.wikipedia.org/wiki/File:Off-axis_optical_telescope_diagram.svghttp://en.wikipedia.org/wiki/File:Off-axis_optical_telescope_diagram.svg