convex and concave shapes, in order to minimize chromatic and spherical aberrations. So why did it take Carl Zeiss so long to bring a microscope like this to market? One explanation can be found in a letter he wrote to a friend of his youth, K.O. Beck, in 1855 [ 8 ]: All the same, you will be surprised to hear that I have not yet had a fl int lens ground for a compound microscope. Do not think that I would not be ready to make further endeavors in this area—indeed I have experi- mented with many other classes of microscope—yet I believe that the usual compositum cannot take us much further, and I have something of an aversion to this relentless rigmarole of trial and error that is so common among us lensmakers, with people such as Oberhäuser attempting to make one good objective lens from among hundreds of lenses. Carl Zeiss had no qualms about working on corrected lenses. His successful market

Figure 5 : Ernst Abbe in 1876 (ZEISS archives).

launch two years later proves that he was up to the task. Yet he was still suspicious of the traditional production methods involving trial and error. He wanted to get to grips with the problem by considering the appropriate theory. He continued his search for a scientifi c solution. It was therefore no coinci- dence that he approached physicist Ernst Abbe (1840–1905) in 1865 to help him ( Figure 5 ). “He found what he wanted … because he sought it out” wrote Abbe 30 years later [ 9 ]. Ernst Abbe grew up in very humble circumstances in Eisenach and studied physics and mathematics in Jena and Göttingen [ 10 ]. Aſt er spending a short time in Frankfurt, he returned to Jena in 1863 to earn his doctorate. In such a small town (estimated population of 7,200), it is very likely that the pair had already crossed paths. T ey got to know one another better when Abbe asked Zeiss to construct instruments for his lectures. We know nothing about what motivated Abbe to turn his attention to physical optics, an area with which he had previously not concerned himself in the slightest. It has been speculated that he may have underestimated the problem of optics in microscope construction and believed that the topic could be dealt with quickly.

Meanwhile, Edmund Hartnack had launched water immersion lenses that were superior to all others. Zeiss could have attempted to simply mimic the design of these lenses. But Abbe’s aim was not only to produce microscopes that were better than the competition—he wanted to tackle the problem by considering the appropriate theory. His approach was thus theory-driven and analytical, and his initial attempt to solve the problem geometrically led only to major setbacks in the beginning. He was only successful once he took the wave character of light into account. From 1872 onwards, all of Zeiss’s microscope optics were based on calculations made by Abbe [ 11 ]. In catalog 19, immersion systems were off ered for the fi rst time alongside new dry lens systems. Homogeneous oil immersion lenses followed in 1879 ( Figure 6 ).

2017 July •

What is now known as Abbe’s theory, which stated that image resolution was related to diff raction eff ects, was a big disappointment as far as microscopists were concerned. It showed that the resolution capacity of light microscopes is limited by the wavelength of light. While Abbe did ruminate on using UV light with a shorter wavelength to push this limit [ 12 ], his musings were initially confi ned to the theoretical realm. It was not until 1904 that August Köhler (1866–1948), who headed the microphotography and projection department at Carl Zeiss, launched a UV microscope. T e fi rst microscope to clearly overcome the light microscope employed a medium with a still shorter wavelength; the electron microscope would not be brought to market by Siemens and AEG until more than 30 years later.

Abbe also revised microscope stand design. In 1877 the

round fi ne-adjustment control knob was replaced by a prism control knob on the large- and medium-sized stands. T e same year also saw the publication of the fi rst bound catalog, which was reprinted in the following year and featured illustra- tions. T is catalog refl ected the considerable progress made in development at the workshop. It included a total of 11 microscope models. Large, powerful instruments were added. T e horseshoe stand was then incorporated into the most important models. A new kind of micrometer movement was introduced in 1886. In terms of appearance, these new microscopes only diff ered slightly from the previous models. Some competitors in the 1870s advertised by saying that their lenses were “not produced as they are in Jena,” which meant that the simple optics produced through trial and error no longer stood a chance. T e year 1879 marked the beginning of the collaboration with chemist Otto Schott (1851–1935) that aimed to produce a better kind of optical glass. A systematic,

Figure 6 : Stand with micrometer movement and tilt from 1882, from the collection of Timo Mappes. Photograph taken by Manfred Stich.


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