I have recently acquired a used but "mint" Sonnar 140mm for my Contax 645. When I manually turn the focussing helicoid in either direction past minimum or maximum focus(inadvertently), there is little resistance. My 2 other lenses, 45 Distagon and 80 Planar, purchased new, have a fair amount of "drag" or resistance when attempting this. I don't do this often, but with the 140, it is very easy to go past these "ends" Do others who have this lens find the same thing, or is mine showing a problem? The resulting pictures are typical Zeiss and I have abolutely no compaints; it performs flawlessly.Is there some sort of clutch mechanism that should be adjusted? Thanks.