This article will outline the development of symmetrical lens designs conventionally described as double Gauss. These include the Zeiss Planar, Lee Opic, and Biotar, as well as the vast majority of normal lenses made from 1896 to the end of the twentieth century. It's not too much to claim this innovation as the most important in lens design for camera systems.
In the appendix “Lenses and Their Makers” Cox lists many symmetrical lenses that were on the market at the time. Pages 484-97 of his book (see my references) contain no fewer than 64 different lens diagrams. But if we restrict the survey to 35mm film cameras, only four of the designs were used by more than one lens. That's remarkable consistency!
Symmetrical lenses
Symmetrical lenses have the stop (aperture) located between two doublets. This design can correct coma, distortion, astigmatism, and chromatic aberration, though spherical aberration and field curvature were both still apparent. In the diagrams below this stop is indicated by the vertical opening, perpendicular to the lens axis.
This form derives from a simultaneous innovation in 1866. J.H. Dallmeyer (1830-83) in the UK developed the Rapid-Rectilinear at the same time that H.A. Steinheil (1832-93) in Germany designed the Aplanat. Wide-angle and portrait variants of the Rapid-Rectilinear were produced. To keep aberrations under control, the maximum aperture was constrained to f/8.
Various other symmetrical designs followed. In 1888 Alvan Graham Clark (1832-97) created the double Gauss for Bausch & Lomb. This was based on doubling the elements in an 1817 telescope design by mathematician Carl Friedrich Gauss. This was perhaps an unusual template to choose, since Gauss' design was never successful enough for production. Neither was Clark's own f/8 lens viable in the marketplace.
In this context it's odd that this lineage of lens development is commonly named after the "double Gauss", as this was a failure and not even the first symmetrical arrangement!
Improvements awaited better materials. In 1885 barium crown glass was created by E. Abbe (1840-1905) and O. Schott (1851-1935) at Jena Glassworks. The immediate application was correcting astigmatism in microscope lenses. But immediately photographic applications were considered. In 1888 Heinrich Ludwig Hugo Schroeder (1834-1903) used this glass in his Concentric at Ross & Co. (London). However uncorrected spherical aberration limited the aperture to an unrealistic f/20.
Success came in 1890 with the designs of Paul Rudolph (1858-1935) at Carl Zeiss Jena. Five and four element purely symmetrical designs were marketed initially under the name Anastigmat, since the design improved on correcting astigmatism relative to earlier attempts. As this term became generally applied to such corrected lenses, Zeiss adopted the unique moniker Protar for marketing purposes. The fastest of these lenses achieved f/4.5.
In 1896 Rudolph created an enhanced 6 elements in 4 group design for the Zeiss Planar f/4. This became the template for many other successful lenses that followed. It is not too much to claim this as the single most important design breakthrough in photography... as Zeiss themselves are wont to do.
Other authors (Cox is one of them) prefer crediting the British firm of Taylor, Taylor & Hobson (Leicester, England), perhaps due to their prevalence in the cinema world. In 1920 they released the Series 0 f/2 lens, more commonly known as the Lee Opic, after its designer Horace William Lee. While elements had changed size and values, it's clear how much the topology owed to the Planar.
Lee updated the design to the Ultra Panchro 50mm f/1.4 in 1927 and the Speed-Panchro 50mm f/1.5 in 1930 or 1931. These were notable for having different front and back elements, hence being asymmetrical. (See the last section for a discussion of this terminology.) You can see that the front is very like a Planar but the back more like the Lee Opic.
Eventually Cooke Optics was spun-off from TTH and continues to this day. Their current products and reputation are still reliant upon the designs mentioned here.
In 1925 designer Albrecht Wilhelm Tronnier at Jos. Schneider & Co. Optische Werke followed the symmetrical mold, creating the Schneider-Krueznach Xenon f/4.3. The following year the improved Schneider-Krueznach Xenon f/1.8 was released for cinema.
In 1927 Willy Walter Merté at Zeiss Jena created a very similar design for cinema under the name Biotar 50mm f/1.4.
Further symmetrical lens design
This section will list the chronological development of symmetrical lenses, beginning with additional 6 elements in 4 group designs:
- 1932: Leitz Wetzlar Summar 50/2
- 1936: Zeiss Biotar f/2 for Ihagee’s Kine Exakta camera, the first widely available SLR
- 1939: Leitz Wetzlar Summitar 50/2
- 1949: Zeiss Biotar f/2 for Volkseigener Betrieb (VEB)’s Zeiss Ikon Contax S
- 1935: Schneider-Krueznach Xenon 50/1.9
- 1935: Schneider-Krueznach Xenon 50/2
- 1950: Voigtländer Ultron 50/2 for Voigtländer Vitessa
Notable 7 elements in 5 group designs were initiated by the Speed-Panchro 58mm:
- 1930 TTH Super Speed-Panchro 58/1.5
- 1959 Carl Zeiss Planar 55/1.4
- 1964 Canon 50/0.95
While Leica pursued six element designs they also released several important 7 elements in 4 group configurations:
- 1939: Leitz Summitar 50/2
- 1949: Leitz Summarit 50/1.5
- 1953: Leitz Summicron 50/2
The following was released for only about a year as an 8 element in 7 group design. It was then replaced by a version that was less expensive to manufacture.
- 1964: Asahi Pentax Super Takumar 50/1.4
The configuration of 7 elements in 6 group became widespread:
- 1965: Asahi Pentax Super Takumar 50/1.4
- 1975: SMC Pentax 50/1.2
- 1975: SMC Pentax 50/1.4
- 1975: Carl Zeiss Planar T* 50/1.4
- 1977: SMC Pentax-M 50/1.4
- …and many more
Contemporary practice
According to Jonas and Thorpe of Leica, the double Gauss design reached its design limits with the Summilux 35mm f/1.4. Created in 1958, at a time when ray tracing had to be performed manually, this lens nonetheless optimised aberration control to a degree that could not be improved with computerisation. At this time glass elements had a spherical profile and hence spherical aberration were an unavoidable quantity.
The next materials innovation was the creation of aspherical elements. Though expensive to produce, optimal use in a design could reduce aberrations to a level previously unheard of. The Summilux 35mm f/1.4 ASPH of 1991 improved on the previous models (at least in technical terms). Since the 1990s computer-aided design, improved materials, and the ability to assemble high numbers of elements have left the simpler designs described above behind.
However this doesn't mean that the Planar / Opic / Biotar / Panchro perform any worse now than they ever did. In fact, photographers increasingly turn to antique lenses for a distinctive character that has perhaps been lost in more technically perfect lenses. Manufacturers are even creating new products to emulate these designs.
Final word on terminology
There is some inconsistency in how the word "symmetrical" is used to describe these designs. Some authors take this to include any design where there are lens elements on either side of the stop. Other authors reserve this term for lenses with exactly the same elements on either side of the stop.
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