Ray tracing is a widely applicable technique for modeling the propagation of light through an optical system. The modeling of light propagation via ray tracing is commonly called geometrical optics.

In sequential ray tracing, rays are traced through a pre-defined sequence of surfaces while traveling from the object surface to the image surface. Rays hit each surface once in the order (sequence) in which the surfaces are defined. Imaging systems are well described by sequential surfaces. Sequential ray tracing is numerically fast and is extremely useful for the design, optimization and tolerancing of such systems. Aberration calculations such as ray fan plots, diffraction calculations, and wavefront aberration calculations can be easily performed using sequential ray tracing.

Many conventional optical systems can be classified as imaging systems. These include photographic objectives, telephoto lenses, microscopes, telescopes, relay lenses and spectrometers.