collimation

Collimation is the process of aligning the components of a beam so that the emitted or propagated rays share a common axis and travel with minimal angular spread. In optics, a collimated beam consists of light rays that are essentially parallel. Collimation is achieved with devices called collimators, which may be lenses, diaphragms, or apertures that remove off-axis rays. A perfectly collimated beam is idealized; real beams have finite divergence determined by source quality, wavelength, and optical quality.

In astronomy, collimation refers to aligning the optical elements of a telescope, particularly telescopes with mirrors. Proper collimation ensures that light from a distant object is focused to a sharp point in the focal plane. Misaligned optics introduce aberrations such as coma and astigmatism. Various tools, including Cheshire eyepieces, laser collimators, and sight tubes, are used to adjust the mirrors.

In particle physics and radiation therapy, collimation describes shaping a beam of charged particles or photons by absorbing or blocking off-axis components. Collimators restrict the beam's cross-section and reduce stray radiation, protecting equipment and patients and improving experimental or imaging results. In radiography, X-ray collimation lowers patient dose and improves contrast by limiting the beam to the region of interest.

Overall, collimation is a unifying concept across disciplines: aligning or shaping a beam to travel along a desired axis with minimal divergence.