09-12-2014, 12:50 PM
One "C" and one "S".
"C":
http://www.sigmaphoto.com/product/150-60...g-os-hsm-c
"S":
http://www.sigmaphoto.com/product/150-60...g-os-hsm-s
"C":
http://www.sigmaphoto.com/product/150-60...g-os-hsm-c
"S":
http://www.sigmaphoto.com/product/150-60...g-os-hsm-s