Nikkor 3.5 - 8.5cm Wide-Zoom

Prototype lens presented by Nikon on the National Photographic Show Convention, Philadelphia in spring 1961. From Nikon Site:

This zoom lens was a revolutionary product insofar as it was the first ever lens of the concave-convex 2-group zoom type which is now the benchmark configuration for today's standard and wide angle zoom lenses. HIGUCHI, Takashi was at the time tackling the development of this new genre, the standard zoom, from two completely different approaches, the 43-86mm f/3.5 3-group zoom type, and the 35-85mm f/2.8 2-group type.
However the 35-85mm f/2.8 zoom was never mass-produced or sold, despite the announcement of its creation. According to the May 1961 issue of Japanese "Shashin Kogyo" ("Photography Industry", pub. Shashin Kogyo Shuppansha) magazine in which the announcement appeared, the lens had an 8-group, 13-element configuration, length of 95mm, maximum diameter of 90mm, weight of 1.1 kg, and a filter attachment size of 82mm diameter, making it a behemoth of a lens.

The lens has a unique arrangement of scews in the mount, instead of three screws in the mount as with other early Zoom-Nikkors, there are six arranged in three pairs. The aperture scale and focal length index are also offset about 45° to the left side. Presumably this is to make them visible to the operator, in the normal position the view would be blocked by the bulk of the lens and metering head on the camera.

Two prototypes are known which differ in some details:

First prototype Narrow finely knurled focus ring marked in feet. Chrome barrel between zoom and focus rings with lens name. This lens was sold at Westlicht Auctions in December 2009.
Second prototype has an all black barrel. The focus ring is wider with lens data engraved in white on the top portion. The focus scale is in m. This lens is currently displayed at the Nikon Museum in Tokyo.

The serial number of one lens is known: 352803, the number is taken from the focal length and aperture. The last two digits suggest at least three examples were made. If the black version is a newer improved prototype, that makes four and possibly more. if anyone is able to obtain the serial number from the lens at the Nikon Museum, let me know!

Development of 3.5-8.5cm zoom at Nikon site
More details at Nikon site at end of 43-86 article
Article at Photography in Malaysia site

First prototype with chrome barrel:

Second prototype with black barrel: