This chapter is from the book
This chapter is from the book
This chapter is from the book
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.
)
Curves Ahead
)
There are two basic types of simple lenses: positive and negative. A positive convex lens causes parallel light rays entering one side of the lens to converge at a focal point on the other side. A negative concave lens causes parallel rays to emerge moving away from each other, as though they came from a common focal point on the other side of the lens. With these two basic shapes, optical engineers have engendered a variety of multiple lenses, which bond two simple lenses with a transparent glue. Simple and multiple lenses go into making compound lenses, which use different combinations of lenses to herd light rays into the corrals of film, eyes, and imaging sensors. Here are some variations on combinations of simple lenses, all of which can show up in the same camera lens.