The invention of the camera in the early 19th century led to an array of lens designs intended for photography. The problems of photographic lens design, creating a lens for a task that would cover a large, flat image plane, were well known even before the invention of photography due to the development of lenses to work with the focal plane of the camera obscura.
Early photographic camera lenses (1800–1890)
The early photographic experiments of Thomas Wedgwood, Nicéphore Niépce, Henry Fox Talbot, and Louis Daguerre all used simple single-element convex lenses. These lenses were found lacking. Simple lenses could not focus an image over a large flat film plane (field curvature) and suffered from other optical aberrations. Their severe longitudinal chromatic aberration meant the light the photographers were seeing (generally yellow light) and the light to which the early photographic mediums were sensitive not converge to the same point, making it difficult to focus.
Charles Chevalier's Paris optical firm produced lenses for both Niépce and Daguerre for their experiments in photography. In 1829Frizot 2008, p. 21., Chevalier created an achromatic lens (a two-element lens made from crown glass and flint glass) to cut down on chromatic aberration for Daguerre's experiments. Chevalier reversed the lens (originally designed as a telescope objective) to produce a much flatter image plane and modified the achromat to bring the blue end of the spectrum to a sharper focus. Reversing the lens caused severe spherical aberration so a narrow aperture stop was necessary in front of the lens. On 22 June 1839, Daguerre contracted Alphonse Giroux (France) to manufacture his daguerreotype apparatus. The Giroux Le Daguerreotype camera used an almost 16-inch (40 cm) focal length reversed achromatic lens with a f/16 stop in front of it made by Chevalier to take 6½×8½ inch (about 16.5×21.5 cm) images.Todd Gustavson, Camera: A History of Photography From Daguerreotype to Digital. New York, NY: Sterling Innovation/Sterling Publishing Co., Inc., 2009. . pp 8-9.Colin Harding, Classic Cameras. Lewes, East Sussex, UK: Photographers’ Institute Press, 2009. . pp 18-19.
Meniscus or 'landscape' lens
In 1804 William Hyde Wollaston invented a positive meniscus lens for eyeglasses. In 1812 Wollaston adapted it as a lens for the camera obscura by mounting it with the concave side facing outward with an aperture stop in front of it, making the lens reasonably sharp over a wide field. Niépce began using Wollaston Meniscus in 1828.Gernsheim 1969, p. 61. Daguerre used this lens in his experiments, but since it was a single-element lens that lacked any chromatic aberration control it was impossible to focus accurately with the blue-sensitive media in the daguerreotype process.
By the end of 1839, Chevalier had created an achromatic version of the meniscus that combined field flattening and chromatic aberration control. The lens had the reverse concave flint glass side facing the subject and an f/16 aperture stop at its radius of curvature, making it reasonably sharp over a wide field of about 50°. Reversing the lens did increase chromatic aberration, but this fault could be lessened by adjusting the achromat to bring colors at the blue end of the spectrum into focus to match the blue-sensitive nature of the photographic emulsion. This design was copied by other lens makers. Because of its large flat field over a wide angle of view and its "slow" f/16 aperture (requiring twenty to thirty minutes for outdoor daguerreotype exposures), this lens came to be known as the "French landscape lens" or simply the "landscape lens".
Petzval Portrait lens
Because the Achromat Landscape lens was quite slow, the French Society for the Encouragement of National Industry offered an international prize in 1840 for a faster one. Joseph Petzval (of modern Slovakia) was a mathematics professor with no optical physics experience, but, with the aid of several human computers of the Austro-Hungarian army, he took up the challenge of producing a lens fast enough for a daguerreotype portrait.
He came up with the Petzval Portrait (modern Austria) in 1840, a four-element lens consisting of a front-cemented achromat and a rear air-spaced achromat that, at f/3.6, was the first wide-aperture portrait lens. It was appropriate for one- to two-minute shaded outdoors daguerreotype exposures. With the faster collodion (wet plate) process developed in the 1850s, a camera equipped with this lens could take one- to two-minute indoor portraits. Because of national chauvinism, the Petzval did not win the prize, despite being far superior to all other entries.
A 150mm Petzval lens was fitted to a conical metal Voigtländer camera taking circular daguerreotypes in 1841. The Voigtländer-Petzval was the first camera and lens specifically designed to take photographs, instead of being simply a modified artist's camera obscura.Wade, Short History. pp 18, 20. The Petzval Portrait was the dominant portrait lens for nearly a century. It had what would now be considered severe field curvature and astigmatism, but It was centrally sharp (about a 20° field of view, or 10° for critical applications), and it quickly drifted out of focus to a soft outer field, producing a pleasant halo effect around the subject. The Petzval Portrait remains popular as a projection lens where the narrow angles involved mean the field curvature is not significant.
The Portrait was illegally copied by every lens maker, and Petzval had a nasty falling out with Peter Voigtländer over unpaid royalties and died an embittered old man. Although the Portrait was the first mathematically computed lens formula, trial and error would continue to dominate photographic lens design for another half century, despite well-established physical mathematics dating from 1856 (by Philipp Ludwig von Seidel [modern Germany], working for Hugo Adolph Steinheil [modern Germany]), to the detriment of lens improvement.
Overcoming optical aberrations
The Achromat Landscape was also afflicted with rectilinear distortion – straight lines were imaged as curved. This distortion was a pressing problem as architecture was an important photography subject early on. In addition, photographs of exotic places (especially in stereoscope formGeorge Gilbert, Collecting Photographica: The Images and Equipment of the First Hundred Years of Photography. New York, NY: Hawthorn/Dutton, 1976. . pp 90-92.) were a popular means to see the world from the comfort of one's home – the picture postcard is a mid-19th century invention.Mason and Snyder, pp 148-149. The distortion got progressively worse as the field of view increased, which meant the Achromat Landscape could not be used as a wide-angle lens.
The first successful wide-angle lens was the Harrison & Schnitzer Globe (USA) of 1862, although with a f/16 maximum aperture (f/30 was more realistic). The lens had a 92° maximum field of view, although 80° was more realistic. Charles Harrison and Joseph Schnitzer's Globe had a symmetric four-element formula; the name refers to the consideration that if the two outer surfaces were continued and then joined, they would form a sphere.
Symmetry was discovered in the 1850s to automatically correct the distortion, coma, and transverse chromatic distortions.Mark D. Licker; publisher, McGraw-Hill Encyclopedia of Science and Technology. 10th Edition. 20 Volumes. New York, NY: McGraw-Hill, 2007. . Volume 1. Aberration (optics), pp 9-14. Volume 4. Chromatic aberration, pp 126-128. There are also decentration aberrations arising from manufacturing errors. A real lens will not produce images of expected quality if it is not constructed to or cannot stay in specification.Cox 1971, pp. 147-150, 198-200.
There are additional optical phenomena that can degrade image quality but are not considered aberrations. For example, the oblique cos4θ light falloff, sometimes called natural vignetting,Norman Goldberg, Camera Technology: The Dark Side of the Lens. San Diego, CA: Academic Press, 1992. . pp 255-257.Lester Lefkowitz, "Lenses: Facts and Fallacies," pp 75-98. Modern Photography, Volume 47, Number 9; September 1983. ISSN 0026-8240. and lateral magnification and perspective distortions seen in wide angle lenses are really geometric effects of projecting three-dimensional objects down into two-dimensional images, not physical defects.
The Globe's symmetric formula directly influenced the design of the Dallmeyer Rapid-Rectilinear (UK) and Steinheil Aplanat (modern Germany). By coincidence, John Dallmeyer's Rapid-Rectilinear and Adolph Steinheil's Aplanat had virtually identical symmetric four-element formulae, arrived at almost simultaneously in 1866, all of which corrected most optical aberrations, except for spherical and field curvature, to f/8. The breakthrough was to use glass of maximum refractive index difference but equal dispersion in each achromat. The Rapid-Rectilinear and Aplanat lenses were scalable over many focal lengths and fields of view for all contemporaneous media, and they were the standard moderate-aperture, general-purpose lenses for more than half a century.
The Landscape, the Portrait, the Globe, and the Rapid-Rectilinear/Aplanat constituted the nineteenth-century photographer's entire lens arsenal.
Aperture stops
It was known in the 1500s that an aperture stop would improve lens image quality. It would be discovered that this was because a center stop that blocks peripheral light limits the transverse aberrations (coma, astigmatism, field curvature, distortion, and lateral chromatic) unless the stop is so small that diffraction becomes dominant. Even today, most lenses produce their best images at their middle apertures, at a compromise between transverse aberrations and diffraction.Dan Richards, "Lens Special: Behind The Glass: Lessons from 444 lens tests." pp 74-79. Popular Photography, Volume 72 Number 2; February 2008. ISSN 1542-0337.
Therefore, even the Meniscus had a permanent stop. Nevertheless, the earliest lenses did not have adjustable stops: their small working apertures and the lack of sensitivity of the daguerreotype process meant that exposure times were measured in many minutes. Photographers did not want to limit the light passing through the lens and lengthen the exposure time. When the increased sensitivity wet collodion process was perfected in 1851, exposure times were shortened dramatically and adjustable stops became practical.
The earliest selectable stops were the Waterhouse stops of 1858, named for John Waterhouse. These were sets of accessory brass plates with sized holes, mounted through a slot in the side of the lens structure.Ray, Photographic Lens. pp 84-85.
Around 1880, photographers realized that aperture size affected depth of field. Aperture control gained more significance, and adjustable stops became a standard lens feature. The iris diaphragm made its appearance as an adjustable lens stop in the 1880s, and it became the standard adjustable stop about 1900. The iris diaphragm had been common in early nineteenth century cameras obscura, and Niépce used one in at least one of his experimental cameras. However, the specific type of iris used in modern lenses was invented in 1858 by Charles Harrison and Joseph Schnitzer.Charles Harrison and Joseph Schnitzer, Diaphragm For Photographic Cameras. United States Patent #21,470: granted 7 September 1858. Harrison and Schnitzer's iris diaphragm was capable of rapid open and close cycles, an absolute necessity for lenses with camera auto-aperture control.