Sigma has indicated that a number of their products require upgrading to work correctly with the Nikon D200 (only #3 has been acknowledged so far by Sigma America). Specifically, (1) the Sigma EF500 DG Super, Sigma EF500 DG ST and the EM140 DG flash units are not i-TTL but will be upgraded to be i-TTL compatible if returned to Sigma in some parts of the world; (2) the 28mm F1.8 DG ASPERICAL RF, 20-40mm F2.8 EX DG ASPERICAL, 24-70mm F2.8 EX DG MACRO, 24-70mm F2.8 EX ASPHERICAL DF, 28-70mm F2.8 EX DG, 28-105mm F2.8-4 DG, and 28-105mm F2.8-4 ASPHERICAL all require firmware upgrades in the lens in order to expose properly with the D200; and (3) all HSM lenses do not support the AF-ON button on the D200 and require a firmware update in the lens.