Many cheap cameras only have one lens that people cannot change or take out. This is called a fixed lens design. More expensive cameras usually have lenses that come off, so anyone can take out one lens and put in another. Depending on what a person wishes to photograph, he or she can use different lenses (objectives) to make a different kind of picture. For instance, to take a picture of something far away a person might use a zoom lens. There are many kinds of lenses.

The study of lenses and how they work is called optics.

For camera lens, it is most difficult to understand the lens design for large format. There is over hundred year effort to provide various ways to get good pictures. These lenses, some used even before World War II, are still usable today. Computers now let engineers make better lenses, though, because they can calculate the way that light goes through the lens and find the best design for each task.