By popular request, ISO 12233 Resolution Chart samples crops have been added to the Sigma 105mm f/2.8 EX DG OS HSM Macro Lens Review page.
Driving the popular request is the huge $200.00 instant rebate currently available for the Sigma 105mm f/2.8 EX DG OS HSM Macro Lens. Get your 100 OS at B&H, Adorama or Amazon.com.
Note that the Sigma 105mm f/2.8 EX DG OS HSM Macro Lens is compatible with extenders.
On a Canon EOS-1Ds Mark III, the lens plus Sigma 1.4x EX DG Tele Converter autofocuses. The lens plus Sigma 2x EX DG Tele Converter does not autofocus on the 1Ds III.