Pic on the left side: Sigma 50-500 without TC, set at f22 (not the best resolution f-stop; sweet spot is f11-f16). Pic on the right side: Sigma 2x TC added, lens set at 250mm (D70 reports 460mm total f.l.) and f22 (lens actually closed to f11 !). This is the sweet spot for the lens itself, so this picture shows teleconverter and Bigma at it's best. However, this pic is still inferior to the "straight" picture shot without the TC.