Understanding Basic Optics Lenses What are lenses? Lenses bend light in useful ways. Most devices that control light have one or more lenses in them (some use only mirrors, which can do most of the same things that lenses can do). There are TWO basic simple lens types: CONVEX or POSITIVE lenses will CONVERGE or FOCUS light and can form an IMAGE CONCAVE or NEGATIVE lenses will DIVERGE (spread out) light rays You can have mixed lens shapes too: For a nice interactive demonstration of the behavior of different shaped lenses from another educational site, click here (the other site will open in a new browser window). Complex Lenses Simple or Complex? Simple lenses can't form very sharp images, so lens designers or optical engineers figure out how to combine the simple types to make complex lenses that work better. We use special computer programs to help us do this because it can take BILLIONS and BILLIONS of calculations. Camera lens This complex lens has 6 simple lens elements - click the small picture to see the whole camera. Zoom lens for home video camera (13 elements) A professional TV zoom lens used to broadcast sports could have 40 elements and cost over $100,000! Magnifying Glass: A simple optical device This diagram (click it to see a bigger version) shows how a magnifying glass bends light rays to make things look bigger than they are. Many optical devices use the same basic idea of bending the light to fool your eye and brain so light LOOKS like it came from a different (usually larger or closer) object. For a really cool interactive demonstration of a magnifying glass from another educational site, click here (the other site will open in a new browser window). .