In 1840 Josef Petzval, a Hungarian, designed a lens for portraiture, and modern lens manufacturers still use his principle as the basis of many of their designs, especially for projection.
The original Petzval lens was made by combining two colour-corrected combinations- very like an R.R. lens with the negative elements facing inwards with a wide space between the two sets of glasses. It was generally used without a central stop and it gave apertures up to f3.6. Today modifications of the original form are used in the Dallmeyer portrait lens and in a number of wide aperture lenses for 8 and 16 mm. movie cameras. More complex types have been developed from it with apertures up to f0.85 and are used for cine photography of the image on X-ray screens.
Petzval lenses are used more for projection than for anything else because over the relatively small field covered, the curved field of the Petzval lens is tolerable. In apertures up to f1.5 or larger they are used for projecting lantern slides and all sizes of cine film. They are also used in epidiascopes.
The great drawback of the Petzval lens is its curved field. This restricts good definition to the centre and explains why Petzval lenses are used for projection, where only a narrow angle is wanted anyway, and for portraiture where, although the angle is greater, loss of definition away from the centre does not matter (and in fact may even add to the pictorial effect of the result).
Josef Max Petzval (1807-91)
Hungarian mathematician. His calculation of a fast achromatic lens in 1840 played a very large part in the rapid development of portrait photography by the daguerreotype process. His portrait lens was of large aperture and achromatic for both optical and chemical rays. Also designed the Orthoscope lens 1857 for landscape and reproduction work. Both these lenses marked a great advance on any previous lenses in use and were widely used for half a century.