How a Lens Focuses an Image
You must remember boring, sunny summer days in your childhood when you took a magnifying glass outside looking for anything flammable. Having spied a dry leaf, you held your magnifying glass between the leaf and the summer sun. Moving the magnifying glass back and forth with the precision of a diamond cutter, you found the exact point where the magnifier’s lens concentrated the sunlight to form an image of the sun on the hapless leaf. Within seconds, the concentrated rays of the sun caused a thin wisp of smoke to rise from the leaf. Then, suddenly, it burst into flame. You had just done the work involved in focusing a camera’s lens, though with more dramatic results.