In 1841, the Petzval Portrait Lens was introduced. Professor Andreas von Ettingshausen brought the need for a faster lens for daguerreotype cameras to his colleague, Professor Petzval's attention, who went ahead in cooperation with the Voigtländer firm to design a lens that would reduce the time needed to expose daguerreotype plates for portraiture. Petzval was not aware of the scale of his invention at the start of his work on the lens, and later regretted not having secured his rights by obtaining letters patent on his invention. It was the first lens to be designed using mathematical computation, and a team of mathematicians whose specialty was in fact calculating the trajectories of ballistics was put at Petzval's disposal by the Archduke Ludvig. It was scientifically designed and optimized for its purpose. With a working aperture of about f/3.6, an exposure only about one-fifteenth as long as that required when using a Chevalier lens was sufficient. Although it produced an acceptably sharp image in the central area of the plate, where the sitter's face was likely to be, the image quality dropped off toward the edges, so for this and other reasons it was unsuitable for landscape photography and not a general replacement for Chevalier-type lenses. Petzval intended his lens to be convertible with two alternative rear components: one for portraiture and the other for landscape and architecture.