Twin Telescope Binoculars
College D’Optique, Paris: 2nd Half 19th Century
Brass, with additional materials and leather case
9.5 long x 4 inches wide (closed)
13 inches long, x 4.25 inches wide (maximum open)
Pair of antique French aprismatic Keplerian binoculars, also called “twin telescope” binoculars. They are of typical form, each side in 3 sections, with a 1.5 inch diameter eyepiece ocular lens attached to an elongated brass telescopic tube within green leather sheaths and with objective lenses on the opposite side. The telescopes are joined by two brass rectangular bars, the central open portion with focus wheel, and with a wheel to adjust the distance of the separation of the two telescopes. They are in their original fitted cowhide brown leather carrying case with strap.
Early binoculars used Galilean optics. They were compact and produced an upright image, but had a relatively low magnification and narrow field of view. Keplerian optics offered higher magnification and a wider field of view, but the image was inverted. To flip the image upright, each tube used additional erecting lenses which lengthened the tubes. Twin telescopes became obsolete when the German manufacturer Carl Zeiss developed commercially available prism binoculars in the 1890s
Condition: Binoculars very good, with working optics, having the usual overall light wear. Case good with the usual overall wear, scuffing, and handling.