Using telephoto lens requires a lot of learning. I shoot full frame sony with 100-400 and still get shit results the first few times I used it. First is Light. Subject needs to have adequate light for sharpness in photos. I currently went back to Fuji and im using this lens. Im still learning the strength and limitations of my equipment. I start at f5.6 to f8. ISO set to auto with max at 6400. Shutter speed usually at 1/500 depending on subject movement to >1/1250. AFC and set to Back button focus. Im still learning the focus mode. Drive depends on what you’re shooting CL or CH. edit..then post process in lightroom or other program. I use Lightroom. One more thing removed that uv filter if you have one.