From pinhole camera to lens camera

With a camera, rays of light come straight from each point on a bright filament, brightly lighted face, or whatever the object is that you are photographing.

The picture on the back of a pinhole camera is made by those rays which go straight through the pinhole. The front wall of the camera stops all other rays.

The sketch shows rays of light from just two specimen points on a lamp filament contributing to the picture at the back. Each point on an object provides rays for a little spot in the picture at the back, a spot slightly larger than the pinhole. With a small enough pinhole, you get a fairly sharp picture.

With a large pinhole, you no longer get a point-for-point copy of the object. You get a patch-for-point copy, rather a fuzzy picture.

When there are several pinholes, each lets through rays of light from every part of the object. So each pinhole leads to a whole picture of the object.

Look at the diagram and imagine what the lens does.

For light starting from a single point, the lens seems to collect up the rays that go through different pinholes. It bends them so that they all run together through a point. That point is called the image.

To know what the lens really does, you must let a lens receive many rays of light and see how it deals with them.