End of European Renaissance and Birth of Telescopes

The emergence of small blown objects in glass originates in Phoenicia, Syria, and Egypt around ~200BC and much earlier for non-blown objects. The magnification effects of transparent materials was known in Antiquity. The blown glass technique had passed through the ages via the Romans and settled in Venice before the first millennium. The first lenses - lense was the Latin name given to a biconvex disk - used as spectacles appear in Italy before 1300 for correcting presbyopia because hand-lenses were unappropriate for writing; this was followed up around 1450 by divergent spectacles for correcting myopia. During the European Renaissance (1400-1600), the crystal- and glasswork of Murano - a small island near Venice -was flourishing. From ^1300, the remarkable developments of Murano's furnaces and the skilfulness of glass blowers allowed the manufacturing of bottles, drinking glasses, chandeliers, polychromatic vases, and ornaments, etc. Around 1550, it had become easy in Murano to procure positive or negative lenses of small optical powers for correcting usual defects of the human eye. In this context, by empirically separating a negative lens from a positive lens, Digges in Pantometrie (1571) and Della Porta in Magia Naturalis (1589) noticed that an object at some distance is seen enlarged; this device is generally considered as the primitive ancestor of the telescope and may be called an "enlarging monocular" (sometimes improperly called spyglass).

Historics on the enlarging monocular are commented in noticeable works by Danjon and Couder [44] and King [85] where the development of early telescope is also described. The construction of enlarging monoculars between ^1608 and 1609 in Holland, is mainly the result of technological advances in fine glass manufacturing and lens polishing in Italy.

Because of technological difficulties encountered in making accurate and efficient metal mirrors, the first telescopes were not reflectors; the refractor telescopes emerged first from transformations of the enlarging monocular by Galileo Galilei. Accounts on the development of telescopes are in Riekher [132] and Wilson [170]. The major milestones in these developments are resumed hereafter.

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