The Magnifying Glass Effect
Let’s go back to that childhood fascination with magnifying glasses that set the scene for the previous illustration. Take a closer look at the hot spot of light created by the magnifying glass. You’ll see that the spot is actually a picture, a small image of the sun. Now, remember how you moved the magnifying glass back and forth until it was just the right distance to start a flame? You were focusing the picture the magnifier made on the leaf. In a camera, you have a lot of controls and sensors to help you focus, but basically you’re still moving the lens back and forth.