The definitive scholarly work on the topic of Imagons was undertaken by Dr. Alfred Scholz, Rodenstock, in 1979.
The following is a précis of his history of soft focus lenses with our apologies for simplification.
In a nutshell, the Imagon lens is based on a 2 element
Achromat. One of the simplest lenses available. Imagons have 2 unique properties. a) Tremendous depth of field due to the fact that light is not resolved at the focal plane but exhibits instead a
zone of focus and b) The ability to stay gently diffused even while sharpening up at small apertures.
Invented by Dr. Heinrich Kuhne (1868-1944) and still in
production by Rodenstock, these lenses represent, in the purists sense, an ideological struggle that took place amongst lens designers prior to current times. Should a lens produce the
sharpest technically correct image possible or should a lens produce an image the natural way that the human eye sees light, which is directly speaking, a low resolution interpretation of reality
with fuzzy edges sharpened and refined by the brain.
The simplest photographs are pin hole images, image sharpness is affected by aperture, but the length of
exposure is too great for general use. Daguerre and Niepce used the simple 1 element Wollaston (1812) Meniscus Lens in their cameras. In essence an eyeglass lens with a diaphram mounted at the
front. This lens caused light to converge at the film plane thereby speeding the imaging process. The Meniscus lens was useful primarily in the near shooting range such as portrait work and was
restricted to small film formats. In 1897 Henry S. Smith produced a 2 element 'semi achromat' in Boston which was used by Alfred Steiglitz for 5x7 and 8x10 formats. This lens produced a
shimmering quality and was initially considered difficult to work with because different shooting circumstances produced wildly divergent results and also because shorter focal length lenses
proved to be too soft.
In the 1920's in Rathenow Germany, Nicola Perscheid, a renowned portrait photographer approached Emil Busch the lens designer, about custom
making a portrait lens. Thus the Aplanat was born.*
The design was inspired by the periscope which is two meniscus lenses, concave to concave, with the addition of a divergent lens cemented in between. Like the Meniscus and Smith lenses before it, softness was variable according to aperture such that by f 8 the image becomes sharp.
After the first world war Voigtlander introduced the Universal Heliar which was produced up until 1970. This design allowed softness at all aperture settings for
large format work with longer focal lengths. In the 30's Ernst Leitz introduced the 9cm Thambar f2.2 for 35mm use. This 4 element design was replaced by the Hektor 125mm f2.5 after the 2nd world
war. Both lenses produced soft images wide open, sharpening up as the diaphram is closed down.
It was in the 20's that Kuhn, who was a photographer, approached
Dr. Franz Staeble, a lens designer in Munich, with his concept of what a lens should be, 'romantic softness without sugariness, blurring without a woolly effect'. The first Imagon hit the market
in 1928 and was called Kuhn's Anachromat. In 1930 the Staeble lens works were acquired by Rodenstock and in 1931 the Imagon was introduced.
The Imagon was available in 3 focal lengths: 200mm H5.8, 250mm H5.8 and 300mm H7.7.
The 200mm has a covering power of 154mm and therefore can be used on 4x5 without movement, although it is
primary adapted to Medium Format cameras. The 250mm has a field of 180mm and is thus a better choice for 4x5. The 300mm covers 5x7 (220mm field).
Focusing an
Imagon is technically challenging and should be done at the taking diaphram due to a focus shift which occurs when closing down. The discs can then be mounted to produce the halo effect for which
the Imagon received it's patent. The subject is usually lit in a contrasty fashion to counter the softness of the lens, however at H 11.5 the Imagon produces a hard shape focus with very little
diffusion. The Imagon is not simply a soft focus lens, but more accurately a lens with variable image production qualities that will reward the student of photography with unique interpretations
of portrait and field work limited only by the imagination.
* The Aplanat lens design was almost simultaneously invented in 1866 by August
Steinheil ( who also gave it its name) and by J.H. Dallmeyer (who named it Rapid Rectilinear). Lens designer Emil Busch died in 1888, so there was no chance for N. Perscheid to meet him in 1920.
My guess is, Dr. Scholz mixed up the Aplanat and the "Perscheid lens" designs. This lens was in fact a soft-focus lens. It was developed around 1920 after specifications of N.
Perscheid and produced by "Emil Busch AG", the lens manufacturing company.
I hope this helps.
Kindest regards
Uli Mayer
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