The paraxial approximation

The paraxial approximation is a simplification used in optics when analyzing light rays close to the central axis of a lens or mirror. It assumes that these rays make small angles with the axis, allowing complex equations to be approximated with easier, linear math. This approximation makes it easier to predict how light behaves without losing much accuracy for rays near the axis. It's commonly used in designing optical systems like cameras and telescopes, where most light rays are close to the optical axis, simplifying calculations and analysis.