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100 Years of Binoculars and Quantitative Microscopy

Pioneering Inventions for Stereomicroscopy and Image Analysis

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.


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Geometric beamsplitting without loss of aperture

Ernst Leitz II was the first to recognize that this problem could only be solved by the principle of physical beamsplitting, which does not affect the performance of the objectives. Leitz realized that a double prism with semi-transparent mirror coating was a suitable solution, as it was the only way to ensure that the rear exit pupil of the objective (responsible for the resolution) remained unaffected when the imaging rays were split. He started experimenting in this field, assisted by Dr. Felix Jentzsch, a physicist who had joined the Leitz works in 1909 and who also invented the modern bicentric darkfield condenser.

The Leitz binocular tube rapidly became the model for all later binocular tubes and is still based on the same optical principle today.

Measuring microscope specimens

In the same year, the Optische Werke Ernst Leitz in Wetzlar surprisingly presented an optical-mechanical device for planimetric determination of quantities in microscope specimens. Through precise, readable movements of the specimen against a fixed eyepiece graticule, this so-called integrating stage, the brainchild of the famous optical designer Max Berek, allowed fast and easy quantitative measurement of extremely small specimen components in incident light and brightfield transmitted light, possibly combined with polarized light. This method replaced the chemical techniques previously used in geology and mineralogy. The movement range of the specimens was 18 x 18 mm. The method also proved useful for other applications such as metallography.

Integrating stage and integrating eyepiece

As brightfield was the only transmitted light illumination technique that could be used with the integrating stage, Leitz additionally launched an integrating eyepiece. This was designed with four or six spindles that precisely moved the eyepiece graticule instead of moving the specimen itself. As the illumination imposed no limitations on the application of the integrating eyepiece in combination with transparent specimens, all of the illumination techniques customary at the time except for brightfield could be used in both transmitted and incident light.

These optical-mechanical image analysis techniques were replaced in the second half of the nineteen sixties by electronic devices with a digital display.

Microscopes with an integrating stage marked the beginning of quantitative microscopy. With precise, readable movements of the specimen against a fixed eyepiece graticule, they allowed fast and easy measurement of extremely small specimen components.


Beck R: 75 Jahre Leitz-Binokularmikroskop. Leitz-Mitteilungen für Wissenschaft und Technik IX:4 (1998) 133–145. Umschau-Verlag Frankfurt/Main.

Rinne F, Berek M: Anleitung zu optischen Untersuchungen mit dem Polarisationsmikroskop, p. 20–223 (1934). Schweizerbarth’sche Verlagsbuchhandlung, Stuttgart.