My graduation to progressive lenses (invisible bifocals), was a recent life-phase that got me surfing for details on presbyopia.  The research struck a note when I found that magnifying glasses had been used to read TV Guide since before 1350 AD.  After that, polishing and grinding techniques allowed for production of small lentil-shaped disks (lenses in Latin) and these could be paired into frames.  Before long, the wearing of convex lenses became a symbol of higher learning.  By 1450, concave lenses for the refractive error myopia had been developed and the stage was set for the invention of the telescope.

     In this regard, spectacle makers were uniquely poised yet there is debate over who first discovered the properties of combined lenses.  A century of evolvement in magnifying strength may still have been needed, for not until 1608 did German craftsman Hans Lipperhey apply to patent "a certain device by means of which all things at a very great distance can be seen as if they were nearby".  The application was denied but Lipperhey, contracted to provide several binocular versions for the Netherlands national government, was generously recompensed.  News of the great invention spread rapidly throughout Europe, and by 1609 three-powered spyglasses, by different makers, were sold in France and Italy.  That was the year an English cartographer, Thomas Harriot, recorded the first telescopic sketch of the Moon - only weeks before an Italian mathematician named Galileo Galilei would pick up the ball and really run with it.

     After building his own three-powered spyglass in June of 1609, Galileo presented an eight powered one to the Venetian Senate. Here, the myth that he invented the telescope began.  With the same principle used earlier in the year to “invent” the microscope, Galileo improved on Lipperhey’s design and claimed it as his sole creation.  Come mid-October and he was exploring the heavens with a twenty-powered instrument.

     His configuration featured a plano-convex objective with a 30-40” (750-1000mm) focal length, and a plano-concave ocular in a smaller tube with a focal length of 2” (50mm) that could be adjusted to focus.  Far from perfect, the lenses in these long thin tubes had a greenish tinge due to the iron content and were usually riddled with tiny bubbles.  While the view was pretty good in the middle, at the periphery it was so poor the objective had to be stopped down to about three-quarters of an inch (18mm). Though the magnification was in the range of 15-20X, the field of view was only 15 arc-minutes.

     It was enough to see Jupiter’s four large moons and, though their present names were suggested by Johannes Kepler, in March of 1610 Galileo documented his discovery and described details of our own Moon in Sidereus Nuncius (The Starry Messenger), a book which would make him famous.  Leader of the field for almost a year, the pack caught up in 1611 by verifying the phases of Venus and with several independent discoveries of sunspots, but by then the Galilean telescope had been popularized.

     A variation on the basic design incorporated two convex lenses.  For increased brightness and magnification, astronomers adapted to an inverted image.  Unfortunately, adding more lenses degraded the view so much it offset any advantage.  Since Galileo’s convex/concave design had progressed to lengths of six feet, and could also be used terrestrially, it remained the scope of choice for the next thirty years.

     As the latter half of the seventeenth century saw larger lenses, with fewer flaws, there was an academic acceptance of the inverted view for the astronomical telescope.  A race to develop more powerful instruments, based on length, soon saw creations exceeding twenty feet.  A good example is Christiaan Hyugens’s scope of 1656.  At twenty-three feet, it had an aperture several inches wide; magnification was near 100X and the FOV was 17 arc-minutes.  As glassmakers gradually eliminated the defects, it followed that multiple lenses were arranged for terrestrial use.

     This marked the end of the road for the Galilean telescope.  In the coming decades it would be passed over for more specialized instruments, some of which would reach enormous proportions, but even when eclipsed by innovation its place in history was bonded forever to the name of Galileo.