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With its twin periscopic extensions swiveled out from the parallel, the Scherenfernrohr provided observers greater depth perception when targeting enemy troops and hardware. (Illustration by Gregory Proch)

In 1894 the German optics firm of Carl Zeiss introduced a new type of prism binoculars, an 8- to 10-power device fitted with adjustable twin periscopic extensions connected by a hinge. Zeiss called its invention the Scherenfernrohr (“scissors telescope”). An observer could position its tubular “ears” upright and parallel to each other or splayed out for greater depth perception, causing objects to appear in modeled relief, strongly distinct from the background. This cross between binoculars and a periscope enabled the observer to remain safely concealed behind walls, trees or other cover with only the upper lenses visible, an advantage with obvious military applications.

In 1905, three years before its patent was to expire, Zeiss produced three large versions of the Scherenfernrohr: the fixed-position Hypoplast, an army-issue variant and a field artillery model. After 1908 other countries produced their own versions of the scissors telescope, which the British nicknamed “donkey ears.” When World War I broke out and the opposing armies burrowed into trenches along the Western Front, the periscopic properties of the Scherenfernrohr soon earned regard as a lifesaving feature. Through World War II the design remained a useful tool for observation, artillery fire direction and a variety of other applications. The postwar West German Bundeswehr did not use Scherenfernrohren, but East Germany’s Nationale Volksarmee did right up until the 1990 reunification.