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Summary

Description
English: The US Patent 4,124,276A, by Yukio Okano, Akiyoshi Nakamura, and Toshinobu Ogura, was filed by Minolta on December 15, 1976 (priority claimed from JP15454075A, 1975 and JP10928176A, 1976) for a "Soft focus lens system". Embodiment 3 of this patent, depicted in Figure 8 with curvatures listed in Table 6, is redrawn here to scale, and matches the configuration (6 elements, 5 groups) of the lens marketed by Minolta contemporaneously as the 85mm f/2.8 Varisoft.

As described in the patent, the lens is divided into three sub-lenses, marked A-I, A-II, and B.

  • Sub-lens A-I is moved by the focusing ring, increasing the air gap between A-I and meniscus lens A-II as the lens is focused to a closer distance. The elements of A-I, a classic Tessar structure, do not move relative to each other.
  • Sub-lens A-II is (relatively) stationary.
  • Sub-lens B affects the amount of spherical aberration, with a larger air gap (as shown in the upper portion of the schematic) resulting in a large spherical aberration and a stronger soft focus effect. When the air gap is minimized (as shown in the lower portion of the schematic), there is virtually no spherical aberration. The size of the air gap also affects the focal length of the entire lens system, so A-I and A-II are moved relative to B when changing the softness setting.
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Author Mliu92

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Captions

"Varisoft" Rokkor lens design, from US Patent 4,124,276A (published 1978)

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26 July 2024

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