Camera lenses bend light by using the principle of refraction, which occurs when light passes from one medium (like air) into another (like glass or plastic) with a different density.
Understanding Refraction in Lenses
- Change in Speed: When light enters a denser medium, it slows down. This change in speed causes the light to change direction.
- Angle of Incidence and Refraction: The amount of bending depends on the angle at which the light hits the lens surface (angle of incidence) and the difference in refractive indices between the two materials.
- Spherical Shape: Camera lenses are typically shaped with curved, spherical surfaces. This curvature is crucial because it precisely controls the angle at which light rays enter and exit the lens.
Converging and Diverging Lenses
- Converging (Convex) Lenses: These lenses are thicker in the middle than at the edges. They bend light rays inwards, causing them to converge at a focal point. These are commonly used to focus light onto the camera's sensor.
- Diverging (Concave) Lenses: These lenses are thinner in the middle than at the edges. They bend light rays outwards, causing them to diverge. These are sometimes used in combination with converging lenses to correct for aberrations or to achieve specific optical effects.
The Role of Lens Geometry
The specific curvature of the lens surfaces determines how the light is bent. A well-designed lens will bend all incoming light rays from a single point in the scene so that they converge at a single point on the camera's sensor. This creates a sharp, focused image.
In Summary
Camera lenses use refraction, taking advantage of the change in speed and direction when light passes from air into glass or plastic. The spherical shape of the lens surface is key to precisely controlling the bending of light to form a focused image.
