Sigma's older APS-C constant f/2.8 standard zoom — pre-OS version without stabilisation.
The Sigma 18-50mm f/2.8 EX DC is an earlier constant f/2.8 standard zoom for APS-C DSLRs, predating the hugely popular OS HSM version. It offered professional f/2.8 speed at a budget price but lacked stabilisation.
Optically good — sharp in the centre with constant f/2.8 providing consistent exposure and subject separation. The pre-OS version lacks stabilisation. EX build quality with quality construction. Adequate for events and general photography at f/2.8.
Available for multiple APS-C DSLR mounts. 67mm filter thread. Approximately 445g — compact for constant f/2.8. No weather sealing. APS-C only. DC designation. Minimum focus distance approximately 28cm.
Available used very cheaply. The 17-50mm f/2.8 EX DC OS HSM added OS and is dramatically more practical. This pre-OS version is only worth considering at very low prices. The OS version is the one to buy.