Perhaps this part of the discussion should be moved to the NHS forum, but it seems to me that Nippon Kogaku/Nikon itself, or @ least some of the men responsible for the Nikon RF, believed that the focal length difference was a factor. Fuketa Masahiko, 1 of Nikon's top designers, is quoted on page 38 in Robert Rotoloni's
The Complete Nikon Rangefinder System (emphasis in original):
The lens mount was very difficult to make. We thought we were the same as Contax but after Nikon One production began we realized we were slightly different. At infinity they are the same but the "travel" was different. This caused long delays.
And Nikon includes the following statement on the historical portion of their corporate web site (originally from an article by Tateno Yokoyuki in "Nikkor Club Quarterly" magazine) regarding the focal length difference (see the section entitled "Truly original?"):
http://imaging.nikon.com/products/imaging/technology/history/rhnc09s-e/index.htm
The leading manufacturer of this type of camera is Ernst Leitz GmbH, which makes direct-view rangefinder cameras. In the beginning, Nippon Kogaku K.K. also thought of developing a screw-mounting camera — just like the ones Leica was making. However, in order to avoid direct competition with other companies already in the market using Nippon Kogaku K.K.'s lenses, rangefinders, and viewfinders, they chose to adopt Contax's bayonet mount system. As this unique mount employed an impartial focusing system, the exterior of the camera resembled that of a Contax. Nippon Kogaku K.K. knew that, based on their experience in the development of Contax mounts prior to W.W. II, and despite its complicated design, they were capable of mass producing the camera. To simplify things a bit, they employed the same flange back (the distance from the mounting surface to the film surface) as Contax. However, since the standard 5 cm Nikkor lens — which was being produced before W.W. II — had the same focal length (51.6 mm) as Leica, they wanted to keep the optical design. So they decided to adapt Contax's mounting shape, while using a Leica-type lens focusing mechanism — the birth of a "combined" mount. Contax's standard lens had a focal length of about 52.3mm, which meant that this Nikon mount could obtain correct focus with both a Contax lens and a Nikon lens at infinity. The extension capability of the Contax lens proved to be insufficient, though, and became rear focused even when adjusted to the rangefinder's double image in the viewfinder. This familiar-yet-original mount required a lens barrel with a design unlike that of Leica or Contax. However, as I mentioned earlier, they had been working with a 35mm camera lens barrel. This resulted in the inside of the telephoto lens becoming complicated, but it wasn't so bad when compared to the camera body.
Again, I'm not an optical expert or engineer & I have no access to primary sources that might contradict my secondary sources, but it seems to me that if there was no difference in focal length, it would have been much easier to simply modify the Leica-style RF mechanism in the Nikon & retain full compatibility w/the Contax system (assuming the back-focus distance is the same, something that has been disputed by Henry Scherer), rather than modifying the entire helical mechanism.
Okay, guys. Let's get to the bottom of this. In the June 1951 issue of Modern photography, John Wolbarst wrote up the most extensive report on the Nikon that any publication had attempted up to that time. He had Bagdonowicz of the NYC optical testing firm test two 50mm f1.4 Nikkors and a brand-new Zeiss 50mm f1.5 Sonnar. The focal lengths reported were: 52.05mm for the Nikkor "A", 51.92mm for the Nikkor "B" and 52.07mm for the Zeiss optic. [page 84, ModPhoto, June 1951]. I do not see how, with the normal variations in focal length that existed from lens to lens even within a given lot, how these differences can be of any significance whatsoever. "Normals" for the Leica may have supposedly aimed at a 51.6mm standard, but if Nikon was trying to match that, they certainly were not getting close.
As I state in my book, the problem was not the helical, but the coupling between the helical and rangefinder optics. The Contax rangefinder is directly coupled via gears from the helical to a pivoting lens in the rangefinder window. The Nikon uses a Leica-type spring-loaded lever that bears against the back of the helical and transfers the movement to a pivoting prism behind the rangefinder window. These different methods of mechanically linking the lens to the rangefinder are, I believe the source of the problem. I do not believe Nikon messed up. They just did what they had to do to make a Contax bayonet mount work with a Leica rangefinder mechanism.
If the helical ends up with a focus difference of around an inch at the closest point, it is because of what the mechanical linkage is telling the rangefinder. In any case, even if the FL standards were what the latter-day critics claim, a difference in focal length of less than a millimeter (less than 1/50th of total length) would not result in a ten degree difference in the travel of the helical. WES
