Harbour Master's Binoculars, mid 19th Century
The binnoculars use Galilean optics with 5X magnification and 53 mm (2.1") diameter objective lenses. The eyepieces can be adjusted over a range of 35 mm (1.4") and a pair of 50 mm (2") long sun-shades can be extended over the objective lenses.
Construction is all brass with quality glass optics. The central focusing adjustment knob looks like it is made from ebony wood but, unfortunately, it has a crack in it. The original green leather barrel coverings have worn away to reveal the underlying brass which has developed a nice patina.
When the sun-shades are fully extended and the eyepieces are fucussed to infinity, the binoculars are 235 mm (9¼") long.
These binoculars are typical of French designs from the mid 19th Century, however they have no markings to identify the maker.
Early attempts to create binoculars using a pair of Galilean or Dutch telescopes date back to Lipperhey in 1608. Various other attempts were reported through the 18th century, but the difficulties of alignment, focusing, and magnification match made reproducible manufacturing almost impossible. It was not until the early 1800s that Galilean binoculars were produced.
By the early 1700s, small Galilean telescopes, usually called spyglasses, prospect glasses, or opera telescopes, had become common. Initially, these handheld telescopes had a single draw and a small field of view. They usually had a magnifying power of 2-3X. By the end of the century, larger optics and achromatic objectives had allowed for increased field of view. Multiple draw spyglasses also were produced.
A major advance occurred in 1823 when J. F. Voigtländer patented the combination of two achromatic opera telescopes or spyglasses into a pair of opera glasses by using a frame with two bridges. J. P. Lemiére of Paris improved upon this design by adding a third bridge between the two eye tubes. The focusing of the two telescopes was then coupled. One very early design was focused by turning the barrel or body of one of the telescopes to drive the motion of the eye tubes. A later approach used a central focusing knob with a threaded screw. This basic design of opera glasses remains in use today. It is quite likely that there were earlier attempts to mount two spyglasses together with a single frame. In early implementations, the bridging frame runs straight between the two telescopes. Later, the bridging frame was curved to allow “nose room” and provide user comfort.
Binoculars - SOLD