Hi! I am half mathematician by education. So here is my math:
Sigma 50-500 at 500 mm plus Sigma 2x extender = 1000 mm. Crop of 50% center portion means like 2x more = 2000 mm. Roughly 1.5 *istD factor = 3000 mm HC> taken on the *istD with a Sigma 50-500 and Sigma 2X extender at 500mm wide HC> open and then cropped to the 50% center portion. equivalent FOV to a 1500mm HC> lens on a 35mm film body. Right? Boris
