Abstract
The story of blurred images begins with the story of imaging, and this got under way 600 million years ago with the long history of the evolution of the eye in living creatures. It continued when the first lenses were made to improve people’s vision, followed by the camera obscura or pinhole camera, used by Renaissance painters. Then came Galileo, who stood on the hills of Florence in 1609 and pointed the first astronomical telescope toward the sky. It was equipped with lenses and brought images to his eyes that no one had ever yet seen.
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Notes
- 1.
Annie Echassoux, Henry De Lumley, Jean-Claude Pecker, Patrick Rocher, Les gravures rupestres des Pléiades de la montagne sacrée du Bego, Tende, Alpes-Maritimes, France. https://halshs.archives-ouvertes.fr/hal-00480210/. The Nebra Sky Disk, discovered in Germany in 1999 and dated to around 1600 BC, is so far the oldest extant representation of the celestial sphere, including the Pleiades. The rock carvings in the Vallée des Merveilles may well turn out to be older. https://en.wikipedia.org/wiki/Nebra_sky_disk.
- 2.
There is no shortage of books about Newton, including the excellent biography by Westfall (1994). The mysterious complexity of this person has been analysed by Loup Verlet in La malle de Newton (Gallimard, 1993).
- 3.
As we have seen, the term ‘visual acuity’ refers to the ability of the human eye to make out fine detail. There exist various measures for acuity. Using the foot as unit of measurement, the acuity is expressed relative to 20/20, this being the best value, although some people with exceptional eyesight can have a slightly higher value. In this book, by a suggestive and practical analogy, we shall also use the word ‘acuity’ to characterise telescopes, measuring their ability to form detailed photographic images. The technical term is ‘angular resolution’, which will be introduced shortly.
- 4.
The mercury column was shorter at the top of the mountain, which showed that atmospheric pressure diminishes with altitude, as Pascal had predicted (Pascal 1957).
- 5.
This angle can be transformed into a length, namely, the size of the Airy disk on a photographic image placed at the focal point of the lens. If the latter has a diameter of 10 cm and a focal length of 1 m, the Airy disk with its coloured rings will measure 5 μm in the image and a magnifying glass would be needed to see it clearly.
- 6.
This may have been the remote beginnings of our hands-on project La main à la pâte, launched in 1995 to introduce primary school children to the pleasures of science. See Charpak et al. (2005). See also https://www.fondation-lamap.org.
- 7.
The Paris Observatory has some beautiful photos taken at the observatory in Meudon at the turn of the nineteenth century by the astronomer Jules Janssen. They show a fine structure at the surface of the Sun, known as granulation, but these images are nevertheless affected by the same limitations on their acuity and the details of the granules that we can now make out by observation from space just cannot be discerned.
References
G. Charpak, P. Léna, Y. Quéré, L’Enfant et la science (O. Jacob, Paris, 2005)
F.M. Grimaldi, Physico-mathesis de lumine, coloribus, et iride, aliisque adnexis libri duo: opus posthumum. Ex Typographia haeredis Victorii Benatii, impensis Hieronymi Berniae, publ. (1665)
P. Léna, La photographie astronomique, in Éclats d’histoire. Actes Sud/Institut de France (2003)
B. Pascal, Œuvres complètes (La Pléiade, Genève, 1957), p. 359ff
R.S. Westfall, The Life of Isaac Newton (Cambridge University Press, Cambridge, 1994)
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Léna, P. (2020). From the Dawn of Time. In: Astronomy’s Quest for Sharp Images. Astronomers' Universe. Springer, Cham. https://doi.org/10.1007/978-3-030-55811-6_2
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