Math question about Nikon helicoid

[antiquark]

Hello all,
In another thread, I discovered that the helicoid for the Nikon RF system was constructed in the camera body. This intrigued me from an engineering perspective, because it permitted the reuse of the helicoid for different lenses, and eliminated the need for each lens to have its own.

However, I'm wondering how that worked with wide angle lenses. The helicoid has distance markings on it. Are those numbers still accurate if you change the focal length of the lens? I plugged a few numbers into the thin lens equation:
http://hyperphysics.phy-astr.gsu.edu...pt/lenseq.html

And it seems that a lenses with different focal lengths would need their own unique helicoids.

(I don't own a Nikon RF, so it's a mystery to me.)

Here's a thread with pictures of helicoids, in case I'm unclear:
http://www.rangefinderforum.com/foru...t=70725&page=2

EDIT:
I found the answer:

http://www.cameraquest.com/conrf.htm

The focusing mount is quite interesting because the focusing helical for the 50mm lenses is built into the body rather than the lens. This design has the benefit of making very small 50mm lenses, but had the disadvantage of what some say is an overly complicated mount. The inside mount is for 50mm lenses, whiles the outside bayonet is for wides and teles.

[Brian Sweeney]

In many ways the Contax/Nikon style helical is more accurate than the Leica counterpart. The RF coupling is rotational rather than translational. The Nikon helical moves ~260degrees from 3ft to infinity. The Contax moves ~270degrees. Leica lenses must translate the motion of the helical to the movement of a 51.6mm lens moving from close focus to infinity.