Part 2.- Here comes the sun
(and I say It’s all right)
In 1926 Ernemann Company, Carl Zeiss and other companies merged into Zeiss-Ikon, and it is not a wild guess to assume that Ludwig Bertele had more resources for the research and development of new objectives.
One year before Ernst Leitz of Wetzlar had successfully released the Leica I establishing the 24 mm × 36 mm negative format on perforated 35 mm movie film as a viable photographic system. To compete in the upcoming camera format, Zeiss-Ikon started to develop the Contax camera system, and Ludwig Bertele was charged with the responsibility of designing the lenses.
The focal length of 50mm was designated as the “standard” for the 35mm format. Technically the focal length of 50mm is a very good compromise between high speed, small dimensions and excellent optical correction. Thus, the Leica featured a fast standard 50mm f/3.5 lens as its primary lens.
Elmar 3.5cm f/3,5
The first approach to the lens was the Elmax, a design based on the Cooke triplet consisting of five elements in three groups with the third group being three cemented elements and with the aperture stop in the first air space. However the Elmax was quickly dropped in favor of the Elmar design which featured four elements in three groups with a cemented doublet in the third group. Apparently the complex three element last component was difficult and expensive to produce and the Elmar design provided a better commitment. By 1930 Leica was already offering their second standard lens the faster Hektor 50mm f/2,5
Hektor 50mm f/2,5
This was the contender that good ol’ Ludwig faced at the time. Not surprisingly, the path that he chose was to design a faster standard lens to beat the Elmar and Hektor in the new camera system. A faster lens meant an important commercial advantage, allowing available light photography at a time of slow film speeds (the fastest film available at the time had a nominal speed equivalent to ISO 50). Bertele proceeded to further develop the second Ernostar design. Starting from his successful six elements in four groups’ configuration, he managed to connect the negative element of the third group with the positive element of the fourth group, thus reducing the number of optical groups to three which effectively decreased objectionable reflections and stray light. Optically, in the second group, the second and fourth elements are high-refractive-index lenses, while the third element is a low-refractive-index lens. This cemented lens offers both the effects of the convex lens of the second element and the concave lens of the fourth element. Consequently the new lens consisted of six elements in three groups, with a single positive lens in the first group, the above stated cemented triplet, and a cemented doublet of negative and positive elements in the rear group.
Sonnar 50mm f/2,0
The lens design succeeded in beating the Elmar by allowing the manufacture of a 50mm lens with a maximum aperture of f/2,0 being at the time the first really suitable high-speed standard lens for 35mm photography.
This new lens design was named ‘Sonnar’, which etymologically derives from the German ‘Sonne’ meaning ‘Sun’.
In 1931 Zeiss Ikon announced the Sonnar f/2,0 to be paired with their new Contax system. But that was not enough for Ludwig Bertele and just within a year he afforded to enhance the aperture of that lens about virtually one f/stop to f/1,5 by replacing the third group with a cemented triplet consisting of two negative lenses and one positive lens in between. Thus in 1932 the super-fast Sonnar 50mm f/1.5 lenses were announced between high praises from the specialists.
Many state that the Contax Sonnar 50mm f/2,0 and Sonnar 50mm f/1,5 were superior to the later introduced Leica equivalent lenses Summar 50 f/2,0mm (1933) and Xenon 50mm f/1,5 (1935). It took almost 30 years to dethrone the Sonnar, as it was only until 1961 with the release of Leica’s second generation Summilux 50mm f/1,4 with an outstanding double-Gauss design that an improved image quality could be attained.
The Sonnar had important features inherent in its innovative design. This was an important achievement in the years prior to lens coating technology:
- The reduced number of air-to-glass surfaces provided advantages for contrast, resistance to lens flare and stray light in the optical system. The lens configuration featured less ghost and provided high-contrast images even in the backlit condition due to the reduced interface with air.
- The lens configuration was suited for high-speed apertures, it was the first lens design with consistent image quality over the whole picture area even wide open. A small number of optical groups meant less light dispersion and good contrast at edges at every aperture.
- Its design provided superior compensation for spherical aberration over the entire image. In addition, it properly reduced coma for broader angles of view even when configured with relatively lower refractive index elements and despite the larger diameter of f/2. Most lens aberrations grow disproportionately when the aperture is doubled, the strong cemented interface on the rear component of the Sonnar 50mm f/1,5 allowed correction on the higher-order spherical aberration which was needed in a lens of the high aperture.
- A typical characteristic of the Sonnar-type lens is high-contrast images with less coma flares even at full-open aperture. By stopping down the lens flare gets disappeared and sharpness is enhanced, further stopping down the lens delivers a sharper and higher contrast image.
The Sonnar design proved to be capable of excellent results and usable for a wide range of applications, since its release in 1931 they were made in focal lengths from 40mm to 300mm. signature 50mm. Companies such as Canon and Nikon created their own Sonnars in the M39 lens mount and in their own mount. Nikon Sonnar’s 50mm, 85mm, 105mm and 135mm helped greatly to build the reputation of the company; they became worldwide renowned after the Korean war thanks to the photos of war correspondents such as David Douglas Duncan for Life Magazine. After being amazed from the quality of the images produced by the 8.5 cm f/2, Duncan visited Nikon’s Ohi Plant to check the performance of Nikkor lenses, and purchased on the spot the 5cm f/1,5 and 13,5 cm lenses.
Nikkor 8.5 cm f/2 Sonnar