An optical train, also called an optical assembly, is an arrangement of optical components (e.g. lenses, mirrors, prisms) to guide a line of sight and/or a laser beam.
[1] For example, the position and angle of lenses may be adjusted to guide a laser through the path required.
Optical instruments like microscopes, telescopes, and DSLRs all have optical trains that guide the incoming light towards a detector or the eye of an observer.
The optical train of a telescope is commonly called an optical tube assembly (OTA) or simply an optical tube.
This optics-related article is a stub.