Review of the APO 100-300mm f/4D EX DG HSM Sigma: Sharp, even at f/4, excellent construction, great value for money.
Review of the ATX Pro 12-24 mm f/4G Tokina. Strengths and weaknesses, links to pro reviews. Conclusión: big bang for your buck.
What means AF-S DX IF ED D G fEE SLR APO APS-C HSM CCD? Dictionary of (digital) photography terms and abbreviations.