Though telescopes have a long history they were only produced in quantities to be widely available in the late 18th century.
Problems of lens polishing, lens composition, and manufacturing were slowly overcome and the telescope became a vital element of seafaring equipment. Superior optics meant that navigation hazards could be identified at longer distance, and in time of war and piracy it meant that approaching vessels could be recognized at longer distances. It also made the use of communications by signal flags practical.
Early telescope construction consisted of barrels constructed of leather, vellum, or wood with the lenses held in place by brass fittings. The one pictured below and found in the National Maritime Museum, Greenwich, London dates from 1775 and is made of mahogany. It measures 35″ closed and when open is 44″ long. The opening holding the objective lens is 66mm, about 2.5″, in diameter. Hardly something you’d want to climb into the rigging holding.
As the science of metallurgy advanced, the telescope barrels of brass became more common. This next telescope, also from the National Maritime Museum, dates from about 1800 and is leather-covered brass some 25″ long when closed and 29″ long when opened. The end holding the objective lens is 44mm or about 1.7″ in diameter.
In the case of the brass telescope, the handiness of lopping some 15 inches off the extended length is a radically reduced field of vision.
Another interesting innovation was the development of the night telescope, or night glass. Using a conventional telescope at night is difficult because the relatively small objective lens did not permit a lot of light to enter the tube and interior lenses which were required to correct the inverted image produced by a simple refracting telescope absorbed part of that light. The result was a telescope with a fairly large objective lens but which produced an image that was inverted,
The below example of a night telescope dates from 1810, it has a leather tube with brass fitting. It measures 28″ long closed and 34″ when extended. The end holding the objective lens is 82mm, or nearly 3.25″.