I recently had the chance to look at the Sigma and Tamron 150-600 lenses. I found the manual focus action on the Sigma 150-600 Contemporary lens to be rather stiff. Sigma said they hadn't really had any complaints about it so I'm wondering if the sample I got was stiffer thanaverage or if it's just a characteristic of the Contemporary lens. The Sports version and the Tamron both had very a smooth manual focusing action. Anyone with a Sigma 150-600 "C" lens have any comments on this?