BASIC LENS

The optical component of the camera is the lens. You can compare this with glasses. It consists out of a curved piece of glass or plastic. The lens takes the light beams and forms these to a real image. The image represents all the light beams from in front of the lens.

How is light formed to an image? The piece of glass in a lens slows down the light it's speed. Light travels much faster in air than in a piece of glass.

Since a lens is curved, some light beams will reach the glass before another and slow down first. When entering the glass, the light will bends in a certain direction. The same happens when the light exits the glass. This will reverse the path of light from an object. 

The light path and the formed image depend on two major factors.

1. The angle of the light beam's entry into the lens
2. The structure of the lens

When you move the object closer or father away from the lens, the angle of the light is changed. This will result in a different image. A lens bends light beams to a certain total degree, no matter the light beam's angle. This total "bending angle" is determined by the structure of the lens.

To focus an image, you turn the lens of your camera. What you actually doing is changing the distance between the lens and the film. The perfect distance is called the focal point.