One hundred years ago, in 1913, the Optische Werke Ernst Leitz in Wetzlar, predecessor of Leica Microsystems CMS GmbH, made two inventions that were to blaze the trail for modern microscopy: the binocular tube and the integrating stage for quantitative microscopy.
Throughout the 400-year history of microscopy, microscopists have always wanted to be able to look at their specimens with both eyes. Optical and mechanical engineers, most of them from France and England, kept devising solutions to this problem, but they had some serious shortcomings as regards resolving power. These early binocular microscopes were designed according to the principle of geometric beamsplitting, whereby the rear exit pupil determining the resolution was split. This halved the numerical aperture of all the objectives used. For differentiated viewing, therefore, microscopists had to resort to the monocular viewing tube.