Dear Nick,
The 40mm 4.0 Distagon lens that you have is the FLE version which has the floating elements. The third ring at the top is for fine adjustment of the floating elements for close range up to infinity. The first setting is from 0.5m to 0.9m, which is equal to a range of 18 inches to 34 inches. The next setting is from 0.9m to 2m, which is equal to 34 inches to 6 feet. The next setting is from 2m to infinity. Depending on the distance of the subject that you are focusing on, you will select one of these settings. Make sure you use a lens hood with this 40 mm Distagon otherwise the lens will not be properly shaded against unwanted light sources.
Lenses designated for use on the Rollei 6008i series are not compatible with the SLX, 6002, or 6006 bodies.
Regards,
Dale