Right Side Up/Upside Down

By James Edgar Hyer

Hold a magnifying glass 1/2″ (13 mm) above a letter on a printed page and observe how the letter appears to be larger. Next, hold the glass about 2″ (5 cm) above the letter and notice how much larger it looks. Then, hold the magnifying glass 1′ (30.5 cm) or more from your eye and look at an object 10′ (3 m) or so away. What do you see?

Instead of appearing larger, the tree or house appears smaller—and upside down! The light that comes from the top and from the bottom of the distant object is almost parallel. The lens in a magnifying glass bends the light so that it eventually comes together after it passes through the lens. If the light travels through the lens and on to a distance beyond the point where it comes together, called the focal point, the light inverts, or crosses over. When the inverted light reaches your eye, the object appears to be upside down. And because the focal point for most magnifying glasses is about 10″ (25 cm), the farther you hold the lens from your eye, the smaller the object appears.

When you look at a distant object, as you move the lens from near your eye to arm’s length, the object “blurs out” when the lens is about 10″ (25 cm) from your eye and then reappears upside down and increasingly smaller as you continue to move the lens farther away.