Lenses: controlling the image
The next step in understanding lenses is to see how the controls on your camera’s lens allow you to alter the image. This introduces focusing scales and lens aperture (including f-numbers). The aperture adjusts image brightness and the range of subject distances you can focus sharply at one setting. It is very important in image-making to know when and how to create total sharpness, or to localize image detail. Some differences between cameras of different format (picture size) start to appear here too.