How a Lens Bends Light
The lens performs multiple jobs when it comes to gathering the light that the camera then shapes into a photograph. The lens frames all the subject matter and determines how close or how far away it seems. The lens controls how much light passes through it, and which subjects are in focus. Framing with a viewfinder and the zoom controls still needs your aesthetic judgment. But with most digital cameras, the lens is happy to do all the focusing entirely on its own. Whether you focus the camera manually or let autofocus do the job, focusing works because of what happens when light passes through glass or plastic.