# Geometric optics

Image formation with a converging lens as an example of a beam path: The object marked on the left as a green arrow can be enlarged on a screen to the right of the converging lens.

The geometrical optics , or ray optics uses the radiation model of light and dealt with it in a simple, purely geometrical way, the path of light on lines .

The model of a beam of light limited on a line does not correspond to physical reality, so such a beam of light cannot be realized experimentally either. Nevertheless, with the help of ray optics , the optical image , which is the main subject of technical optics , can often be described with sufficient accuracy.

If geometrical optics are restricted to rays that cut the optical axis very flat, what is known as paraxial optics is available. Closed mathematical expressions for mapping equations can be found for this. However, this method is mainly only used when you want to get a quick general overview before carrying out extensive investigations in more detail.

Geometrical optics can be understood mathematically as a limit case of wave optics for infinitely small wavelengths of light. However, it also fails in this case if the conditions for rays with high energy density or close to the border to shadow (no light) are to be investigated.

## Axioms of Geometric Optics

Fermat's principle can be seen as the most general basis of radiation optics. It leads to the first two of the following axioms .

• 1st axiom: in homogeneous material the rays of light are straight.
• 2nd axiom: At the boundary between two homogeneous isotropic materials, light is generally reflected according to the law of reflection and refracted according to the law of refraction .
• 3rd axiom: The path of rays is reversible, the direction of light on a ray of light is irrelevant.
• 4th axiom: the rays of light cross each other without influencing each other.

## Applications

The main field of application of radiation optics is the treatment of imaging by optical elements, devices and systems such as lenses , glasses , objectives , telescopes and microscopes .

The ray tracing process in 3D computer graphics is also based on the laws of geometric optics.

The mirages caused by a layer of hot air over sunlit asphalt and other natural phenomena can also be explained by applying this principle.

## Limits

Effects that cannot be described by geometric optics include:

However, some methods of geometric optics, in particular matrix optics, are transferred to the concept of Gaussian rays , which partly takes into account the effects of wave optics .

## Further information

• Introduction to ray optics Detailed page about ray optics with many examples, pictures and experiments

## Individual evidence

1. a b c Heinz Haferkorn: Optics. Physical-technical basics and applications. 3rd, revised and expanded edition. Barth, Leipzig a. a. 1994, ISBN 3-335-00363-2 , p. 35.
2. a b Heinz Haferkorn: Optics. Physical-technical basics and applications. 3rd, revised and expanded edition. Barth, Leipzig a. a. 1994, ISBN 3-335-00363-2 , p. 11.
3. Heinz Haferkorn: Optics. Physical-technical basics and applications. 3rd, revised and expanded edition. Barth, Leipzig a. a. 1994, ISBN 3-335-00363-2 , S. 157th
4. Heinz Haferkorn: Optics. Physical-technical basics and applications. 3rd, revised and expanded edition. Barth, Leipzig a. a. 1994, ISBN 3-335-00363-2 , p. 180.
5. Heinz Haferkorn: Optics. Physical-technical basics and applications. 3rd, revised and expanded edition. Barth, Leipzig a. a. 1994, ISBN 3-335-00363-2 , p. 184.
6. a b Heinz Haferkorn: Optics. Physical-technical basics and applications. 3rd, revised and expanded edition. Barth, Leipzig a. a. 1994, ISBN 3-335-00363-2 , p. 37.