Joseph Petzval - Discoveries and Inventions - Optics

Optics

Petzval's greatest achievements lie in his work with geometric optics. In 1839, Louis Daguerre presented the Daguerreotype, the first commercially successful photographic process. Fox Talbot's calotype was discovered earlier but did not enjoy commercial success. Petzval learned of the invention from his friend, Viennese professor Andreas von Ettinghausen. The daguerreotype was problematic in that it required exposure times as long as 30 minutes to create a portrait. With Ettninghausen's urging, Petzval set up a workshop and laboratory at Kahlenberg in Vienna and, after six months of complex computations, produced designs for improved objective lenses for both portraiture and landscape photography. Because the artillery was one of the few occupations that used advanced mathematical computations at the time, Archduke Ludwig lent eight artillery cannoners and three corporals to the computational efforts. The calculations these men carried out in tandem with each other have been regarded as an early (albeit human) example of a parallel computer.

Petzval's portrait objective lens (Petzval Porträtobjektiv) was an almost distortionless Anachromatischer vierlinser (double achromatic objective lens, with four lenses in three groups). The luminous intensity of this flat "portrait lens" was substantially higher than the daguerre standard of 1839, the Wollaston Chevalier lens (f/16). The screen f/3.6 with a focal length of 160 mm made crucially shorter exposure times possible — using exposures of only about 15 to 30 seconds compared to the 10 minutes previously. Thus, snapshots became possible for the first time.

The portrait objective lens consisted of a cemented double lens in front (f/5) and a double lens with a gap in the back. The rear double lens was necessary for the correction of spherical and coma errors. The Chevalier lens used two cemented double lenses, but was immediately replaced by the Petzval lens, so that the Petzval Porträtlinse was the first cemented lens in widespread use. The first portrait objective lenses were rather small and had a diameter of 2.6 cm. The 1856 Petzval lenses produced by Dietzler had a diameter of 15 cm and a weight of 15 kg, with which one could make portraits measuring 33 by 42 cm.

In 1840, Petzval allowed the Viennese entrepreneur Peter Wilhelm Friedrich von Voigtländer to produce the lens for a one-time payment of 2,000 guldens, without a patent or a contract, which led later to a lasting controversy between Petzval and Voigtländer. Voigtländer, who had confirmed the process through his own calculations, produced a prototype in May 1840 and began production of the lens for the daguerrotype cameras in 1841, making a fortune in the process. The thermionic cameras were made from brass, using round daguerreotype plates which exposed a diameter of 8 cm. In 1841, 600 of these cameras were manufactured and sold at a price of 120 guldens. Voigtländer received a medal at the world exhibition in Paris for this achievement. These first metal-body cameras were prototypes of today's modern cameras. It took another 50 years until an improved camera became available. Petzval's portrait objective lens was used into the 1920s (often under other names) in cameras and is used today in projectors. The lens played an important role in the development of photography and cinematography.

Even with all its apparent improvements, Petzval was dissatisfied with the lens and, after some improvements, left it for others to produce and patent. The camera with the new landscape objective, produced by Dietzler, possessed a light foldable chamber with double bellows. Petzval never made a commercial profit from the lens.

Among Petzval's other works are the invention of opera glasses, lens system calculations that led to the perfection of a telescope and microscope (1843), computations for efficient binoculars, and construction of new floodlights (1847). His plan for the construction of lighting systems for ships on the Danube could not be carried out, however. His special mirror lamp (Petzval lamp), which made possible a maximum utilization of light energy, was used particularly for the bright projectors developed by Petzval. Petzval can also be regarded as the inventor of the modern unastigmatic lens system, based on records from his estate. About 1860, Petzval conducted photogrammetric measurements using equipment he had designed. He also proved scientifically that glowing solid compounds emit more light than burning gases. Carl Freiherr Auer von Welsbach later applied this principle to the gas lamp he designed.

Petzval's achievements are used today in cinematography, astronomy, and meteorology. The Astro-Petzval-Objektiv lens is used in astronomy. This objective made a distortion-free illustration of a large part of the sky, as well as permitting photographing of galaxies and star fields. German optics companies (Töpfer, Voigtländerkorrigie, Zeiss) produced the Petzval objective lens until the 1940s. Petzval's largest contributions to optics are his theoretical bases for the construction and correction of optical lens systems. He carried out fundamental work for the theory of aberration in optical systems. A few central terms of this field were later named after Petzval:

  • The Petzval surface is the generally curved image plane of an unadjusted optical system.
  • In the case of adherence to the Petzval condition the Petzval surface is even.

To the regret of physicists, Petzval never released a prepared multi-volume optical work.

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