The main optical components that are part of an optical system include
• Lens: An optical device that transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element.
• Singlet: A simple lens consisting of a single simple element. See Fig below:

• Doublet: A type of lens combination comprising two simple (singlet) lenses, cemented or attached to each other (air spaced). Doublets are used to correct chromatic aberrations. See Fig. below.

• Triplet: A type of lens combination comprising three simple (singlet) lenses, cemented or attached to each other (air spaced). Triplets are used to correct chromatic aberrations. See Fig. below

• Prisms: A transparent optical element with at least two polished flat surfaces that refract light and have an angle between them. See Fig. below:

• Window: A transparent optical element with two flat and polished parallel surfaces for transmitting light of a particular wavelength range of interest (visible and infrared). The window is used as a cover to protect the inner optical elements or as a substrate to produce filters.

• Dome: A transparent optical element with bent parallel (in most cases) polished surfaces that is used as a cover to protect the inner optical elements. A dome with no surfaces that are not parallel behaves like a lens.

• Filter: An optical element that selectively transmits light in a specific wavelength range. The filter is usually implemented as a plane material.
The material can be specially colored for a needed wavelength or made of transparent clear material that is coated to get the needed filter characteristics (selective transmittance or blocking ranges).

• Beamsplitter: An optical element or device that splits the incoming beam of light in two. The split is typically performed with one of three implements:
– A cube comprising two triangular cemented prisms,
– A half-aluminized mirror on a two-surface, polished optical material, or
– A dichroic optical coating.

In all cases, the optical reflected or transmitted surfaces are coated to increase the transmittance or improve the other optical characteristics.

• Mirror: An optical element that reflects light. The reflection is typically made by a metal coating (e.g., aluminum, gold, or silver) on flat or curved surfaces. For special applications, the reflection can be made by a metal (e.g., aluminum) polished surface.