Sony has announced the FE 100-400mm f/4.5 GM OSS, a new professional-grade telephoto zoom lens designed for wildlife, sports, and photojournalism. This marks the first upgraded G Master lens not to adopt a “Mark II” moniker. It’s an interesting choice, as most photographers will likely consider the new 100-400mm f/4.5 GM OSS a direct replacement for the 100-400mm f/4.5-5.6 GM OSS. However, it is not the same situation as the Sony 24-70mm f/2.8 GM II or 70-200mm f/2.8 GM OSS II, as the new telephoto zoom lens adopts a different aperture. The move to a constant f/4.5 aperture means the lens is two-thirds of a stop faster at the long end than before, offering better subject separation and improved light-gathering at essential telephoto focal lengths. It’s not the only thing about the new lens that is constant, as it also features an inner-zoom design, meaning it doesn’t extend in length as the photographer zooms.…