In my previous articles I introduced the Olympus Zuiko 85mm and discussed the thorny problem of variants. This post will conduct a thorough examination of the optical formulas that Olympus deployed and their relationship to the classic Ernostar and Sonnar designs.
Searching for patents
I thought the most logical next step was to search for patent applications and see which matched the lens diagrams as supplied by Olympus literature.
The best possible renderings of the optics were obtained from two sources. Olypedia has a scan of the 6/4 diagram from a German instruction booklet dated 1973. User eggplant_ on Flickr provides a high resolution scan of the 5/4 design from an undated Olympus lens catalog.
For consistency with the remainder of this series, I redrew these designs in my house style. This enables us to clearly examine similarities and differences with important historical precedents.
The patent search proved as surprising as anything else in this article. Restricting myself to an appropriate date range and the assignee "Olympus Optical" I eventually found:
- US patent 3848972 “Large-Aperture Telephoto Lens” by Sumio Nakamura, 11 April 1973
- US patent 4063802 “Telephotographic lens system having short total length” by Toshihiro Imai and Yoshitsugi Ikeda, 14 July 1976
I have strong confidence that these correctly match the lens in question since the diagrams conform exactly to what Olympus published. The first patent makes clear that the fourth element can float to correct for aberrations (astigmatism and coma) at short distances. This is an innovation for a telephoto lens that would otherwise optimise quality only at infinity. The second patent further specifies the lens as f/2 and “80mm or so”. (The floating element is now the third.)
What is surprising is that the first patent is dated 1973, a year after the lens in question was released to market. To confirm, I continued my search back through time to the very first Olympus photographic lens patents but found no others that matched the 85mm. The only logical conclusion is that the firm applied for intellectual property protection in a tardy manner.
The second patent was dated 1976 and the lens design in question was released in 1979, which is a reasonable timeline. I note that the "short total length" of the lens is here claimed explicitly, unlike the first patent. Indeed this lens vies with the Carl Zeiss Sonnar T* 85mm F2.8 for Contax-Yashica mount (as previously documented).
Relationship to Sonnar
Jason Schneider included this lens in his "10 Exceptional Zuiko Lenses in Olympus OM Mount" (Rangefinder Forum, 27 November 2020). He notes that V1 is "a bit soft wide open, and more prone to flare, but some claim it’s better for portraiture". The redesign is "sharper across the field at f/2, delivers images with higher contrast overall, and has better correction for chromatic aberrations".
In another useful article from 2020 David Braddon-Mitchell provides capsule reviews of the entire OM line. He repeats the common opinion that the original design has a “true sonnar” look. The relationship of the OM 85mm to the famed Sonnar design pattern is worth elucidating.
There are several places where we can read histories of the Sonnar lens, but I will use Kingslake's 1989 volume A History of the Photographic Lens. The innovations of Ludwig Bertele (1900-85) are usually simplified into two design threads.
First comes the Ernostar f/2 of 1923, designed for the Ermanox camera. This had two cemented doublets in a 6/4 design with elements on either side of the aperture stop. But his second Ernostar design had a cemented triplet and the third had only one doublet, no triplet. So that's three quite different geometries in two years, not even taking into account differences in the element shapes, refractive indices, etc.
In 1931 Bertele patented his first Sonnar. This had six elements in three groups with a distinctive cemented triplet before the stop and a doublet after. Yet the following year an F1.5 Sonnar had a 7/3 formula with two cemented triplets. Much later the Zeiss Jena Sonnar 180/2.8 was 5/3 but again with a triplet.
In both cases, Ernostar and Sonnar, it's unclear what the key features are that define these templates.
It's now worth looking at the aforementioned Carl Zeiss Sonnar T* 85mm f/2.8 from 1975. This is described as 5 elements in 4 groups in the official literature, although the diagram incorrectly shows an air gap between the last two elements. (This contradiction has been corrected in my diagram.)
(I tried to find the designer or patent for this lens with no luck. Can anyone help?)
We observe that the five elements that remain from the original Sonnar design are similar in geometry, and we retain the cemented doublet. This is fundamentally similar to Bertele's later Sonnars despite not having the triplet of the original.
Let's compare the OM 85mm starting with the Nakamura 1973 design. It does not have a cemented triplet, so isn't like the original Sonnar. But it does bear a distinct resemblance to Bertele's 1923 work. There's a cemented doublet and the distinctive fourth element. The second doublet has moved past the stop and the initial surface is planar. Though we can recognise genes from the Ernostar family, it's quite a unique design. It may render like a Sonnar but it's not a Sonnar.
The Imai and Ikeda 1976 design effectively combines elements 2 and 3, while retaining the overall lens shapes of the original optic to a significant degree. It is definitely a Sonnar of the 1970s. In fact, it is quite similar to the Carl Zeiss lens we just examined, which had precedence. It's unlikely that there was sufficient time for Olympus to actually copy Zeiss, so this is likely a case of convergent evolution.
As time went on, Sonnar lenses lost popularity to derivations of the double Gauss formula, as outlined in a previous article. When Zeiss revived the use of "Sonnar" to describe their telephoto lenses they were using the term for its marketing spin and not for any accuracy in describing the optics.
But, as I hope this analysis makes clear, there is very little to qualify a given design as a Sonnar or Ernostar. To list the characteristics:
- total element count of five or six
- first element is a thin convex-planar
- second group is a single element or a cemented doublet in a thick convex-planar shape
- third group (element three or four) is plano-concave
- then the aperture stop
- final group is a cemented doublet, usually planar-convex with concave-planar
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