Send us Fan Mail The focal length you use to take a photo will significantly affect the photo you create. It will determine what is in a photo, what is not in a photo, how small or large the elements of the photo are, and how the elements in your photo relate to each other. The focal length you use will also determine the depth of field, or as I like to call it, depth of sharpness, that there is in a photo. So, if you want to learn how to use focal length to create better compositions, ...