The Fifth Tale concerns the AI Nikkor 105mm f/2.5 lens.
The history of the Nikkor 105mm begins quite some time ago, tracing back to the S-type camera and the Leica screw mount. The first NIKKOR-P 10.5cm f/2.5 was designed by WAKIMOTO, Zenji in 1949, and released in 1954. At that time, it was the fastest lens available in the 100mm class.
It shared popularity with the NIKKOR-P 8.5cm f/2 lens released in 1948, and established itself as a best-selling lens. Offering superior optical performance from the initial design, the optical systems developed for this lens was continued on into the Nikon F era. The initial design used Sonnar type optics (5 lenses, 3 groups). As you can see from the cross-section in Fig. 1, the thick lens included a group made of three lenses cemented together, and offering sharp, solid images. This optical system was continued for about 17 years until the 1970s, thanks to the accurate design concepts and superior optics design implementation.
In 1971 the lens underwent fundamental design changes, emerging as the Nikkor Auto 105mm f/2.5. The optics were designed by SHIMIZU, Yoshiyuki, who was one of WAKIMOTO's disciples. He designed a large number of lenses from the early Nikkor Auto through AI Nikkor, and was also active in designing optics for diverse other applications, including object lenses for microscopes. He was active as a designer until quite recently, and still comes to Nikon as an educator, and he has taught me much since I first entered Nikon. In fact, he is probably one of the most experienced people at the company.
The design for the 105 mm f/2.5 was completed in the winter of 1966. The design proposal for this best-selling mid-range telescopic lens was continued for three generations, from the Nikkor Auto to the New NIKKOR, the AI Nikkor and then to the AI-S Nikkor. And surprisingly enough, the AI Nikkor 105mm f/2.5S being sold now still uses the same basic design: a design on the market for 34 years. We will enter the 21st century in about half a year, and the superior performance of this lens is proved by the fact that the basic design required no changes over 34 years.