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. Around 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