Overcoming Optical Aberrations
The Achromat Landscape was also afflicted with rectilinear distortion – straight lines were imaged as curved. This was a pressing problem as architecture was an important photography subject early on – buildings do not move, making them popular to photograph with the early slow processes. In addition, photographs of faraway places (especially in stereoscope form) were a popular means to see the world from the comfort of one's home – the picture postcard is a mid-19th century invention. 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 (92° maximum field of view; 80° was more realistic) lens was the Harrison & Schnitzer Globe (USA) of 1862, although with f/16 maximum aperture (f/30 was more realistic). Charles Harrison and Joseph Schnitzer's Globe had a symmetric four element formula – the name refers to the fact that if the two outer surfaces were continued and joined, they would form a sphere.
Symmetry was discovered in the 1850s to automatically correct three (distortion, coma and transverse chromatic) of the seven major lens aberrations (five monochromatic "Seidel sums": spherical, coma, astigmatism, field curvature and rectilinear distortion; plus two chromatic: axial and transverse ) that prevent the formation of sharp images by simple lenses. 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. The more complex the design, the more sensitive it is to improperly polished or aligned elements.
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, 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, that corrected most optical aberrations, except for spherical and field curvature, to f/8. The breakthrough was to use glasses of maximum refractive index difference but equal dispersion in each achromat. The Rapid-Rectilinear and Aplanat were scalable over many focal lengths and fields of view for all contemporaneous film formats, and were the standard moderate-aperture, general purpose lenses for over half a century.
The Landscape, the Portrait, the Globe and the Rapid-Rectilinear/Aplanat constituted the nineteenth century photographer's entire lens arsenal.
Read more about this topic: Camera Lens, History and Technical Development of Photographic Camera Lenses
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