Focal length on a camera is the distance between the center of a convex glass lens element and the focal point of the lens — the point where rays of light meet, or converge. In this case the focal point on a camera is the sensor.
Lenses work by bending light through a series of optic elements. The optical elements are fine tuned so they work together to produce a sharp image. These optical elements are made from all kinds of different materials set up in different arrangements, they consist of concave and convex glass. There are two types of lenses, virtual lenses and real lenses. 'Virtual' lenses are the most common. They focus on anything that is beyond the focal point of the image. Here's a diagram:
Lenses work by bending light through a series of optic elements. The optical elements are fine tuned so they work together to produce a sharp image. These optical elements are made from all kinds of different materials set up in different arrangements, they consist of concave and convex glass. There are two types of lenses, virtual lenses and real lenses. 'Virtual' lenses are the most common. They focus on anything that is beyond the focal point of the image. Here's a diagram:
The second most common type of lens is one that produces a 'real' image that's why they are called real lenses. They have a simpler construction than the virtual lenses. They focus on anything that is closer or equal to the camera than the focal point. They produce a more realistic image as their name suggests. Lenses that fit into this category are usually prime lenses, like the ones that the school has. The school has 40mm prime lenses, these are one of the simplest lenses because they don't require as many moving parts as the zoom lenses do, they only need a focal element that moves to change focus. Here's a diagram of a real lens: