The RF 100-400mm f/5.6-8 IS USM is a favorite for value-conscious shooters or photographers who want an affordable, small, and light option in their kit. Sony FE 100-400mm f/5.6-8 OSSThis week, Sony released a direct competitor to Canon with the FE 100-400mm f/5.6-8 OSS. The Sony FE 100-400mm f/5.6-8 OSS has a solid level of weather sealing, which the Canon RF 100-400mm f/5.6-8 IS USM lacks. Sony FE 100-400mm f/5.6-8 OSS BreakdownAt 100mm, the Sony ever so slightly outperforms the Canon in the center of the frame. Canon RF 100-400mm f/5.6-8 IS USM BreakdownAt 100mm, you see a gradual falloff of both detail and contrast across the frame.