hi david... I believe all 50mm and 65mm lenses for the rb have a floating element (possibly the rz as well?). I own an original rb67 pro (as well as the original 50mm lens, the photographer sold me the whole set including original instruction manual)... and the 50mm has a floating element... Instructions state...
"-Instructions for the 50mm Lens
This lens has a built-in floating system which moves a portion of the lens system to the front or rear, according to the photographing distance, in order to obtain sharp resolution to the picture circumference.
[picture here pointing to the depth of field scale and floating ring (located just above the shutter speed ring)]
Focusing and photographing method
1. As with a standard lens, adjust focusing by turning the focusing knob on the camera body.
- Merely turning the floating ring will not produce accurate focusing.
2. Next, read the distance to subject, set the distance scale of othe floating ring to the center index mark (red dot), and then take a picture.
- The floating ring may be turned to set the distance scale either before or after focusing.
- When turning the foating ring, a portion of the lens system is shifted to the front or rear; however, no variations can be observed on the ground glass focusing screen.
3. Note the depth of field by observing the depth of field scale on the front frame of the lens, or on the ground glass focusing screen by depressing the depth of field preview lever.
When placing emphasis on spur-of-the-moment snapshots, set the infinity mark (red) of the floating ring to the center index mark (red) when the distance to subject is from infinity to approximately 7ft. (2m.), a sufficiently sharp image can b obtained merely by setting 3.3ft/1m (red) to the index.
-In the case of close-up photography nearer than 3.3 ft. (1m.), set the floating ring to 3.3 ft/1m, then stop down the lens as much as possible.
- The distance to subject implies the distance from the film plane to the subject."
The bold part is not in bold in the original text... just so you know.
ps. "when using the 50mm lens closer than 3 1/4 feet (1 meter) it is necessory to use a lens aperture of f/16, or smaller, in order to obtain satisfactory lens performance"
it says necesory not necessary.