There are two main types of optical systems: reflectors and the refractors.
The group of reflective optics consists mainly of mirrors, which are highly polished, highly reflective surfaces of an opaque body.
In the group of refracting optical systems are diopters, which are parts made up of two transparent media separated by a regular surface. When conveniently combined diopters function as useful optical tools such as lenses and prisms.
Stigmatic, aplanetic and orthoscopic optical systems
- An optical system is stigmatic when each object point combines only one image point.
- An optical system is aplanetic when a flat frontal object also combines a flat frontal image.
- An optical system is orthoscopic when an image is conjugated similar to an object.
The only stigmatic, applanetic and orthoscopic optical system for any position of the object is the flat mirror.