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 judg-
ment. 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.
How a Lens Bends Light
When light bounces off an object,
thereflectedlight spreads out
equally in all directions.1
Light travels at slightly different speeds
depending on whether it’s passing through
plastic or glass or some other transparent
medium, such as air or water.2
30 PART 2 HOW DIGITAL CAMERAS CAPTURE IMAGES