When setting up an image, the aperture and lens you choose makes a big difference. It’s important to know when to isolate your subject by shooting with a large aperture like f/2 or when to stop down to capture more of the scene with a small aperture like f/16.
Experimenting in aperture priority mode can help you visualize how changing the aperture affects both your subject(s) and your background. These exercises will help you understand how your area of focus changes as your aperture changes and also how using a different lens drastically changes the affect.(…)