Bacteriologist Robert Koch was given the company's 100,000th microscope in 1907. In 1887 the 10,000th microscope was shipped, four years later the 20,000th, and in 1899 the 50,000th was completed. By 1880, the company had reached an annual production numbering 500. Leitz microscopes improved on other models of their day in several ways, including lighting and optics, particularly with orthoscopic eyepieces. The microscopes were produced for biomedical as well as industrial purposes, including mineralogy. Consulting with his clients, he continued to refine the microscopes to their needs. Leitz introduced serial production, raising sales volume rapidly after 1871. Initially, Leitz was a part shareholder of the business (in 1865), but took over as sole owner in 1869 and continued it under his own name. He was trained as an instrument maker for physical and chemical apparatus and had several years' experience making watches in Switzerland. (1843–1920) from Baden arrived at Wetzlar in 1864 and entered service at the Optisches Institut. Following his early death on, his widow continued the business he had left behind, the 'Optisches Institut' (optical institute). The ocular was capable of rendering an image with the correct perspective, free of the distortions typical of other microscopes at that time.

1922.Perea-Borobio CollectionĬarl Kellner, mechanic and self-taught mathematician, published his treatise Das orthoskopische Ocular, eine neu erfundene achromatische Linsencombination ( The orthoscopic ocular, a newly invented achromatic lens combination) in 1849, describing a new optical formula he had developed.

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