"Collimation" refers to all the optical elements in an instrument being on their designed
optical axis. It also refers to the process of adjusting an optical instrument so that all its elements are on that designed axis (in line and parallel). The
unconditional aligning of binoculars is a 3-axis collimation, meaning both optical axis that provide stereoscopic vision are aligned parallel with the axis of the hinge used to select various
interpupillary distance settings. With regards to a telescope, the term refers to the fact that the optical axis of each optical component should be centered and parallel, so that collimated light emerges from the eyepiece. Most amateur reflector telescopes need to be re-collimated every few years to maintain optimum performance. This can be done by simple visual methods such as looking down the optical assembly with no eyepiece to make sure the components are lined up, by using a
Cheshire eyepiece, or with the assistance of a simple laser collimator or
autocollimator. Collimation can also be tested using a
shearing interferometer, which is often used to test laser collimation. Collimated optical systems are also widely used in flight simulation. Full-motion simulators often incorporate collimated displays to present out-the-window visual scenes that appear geometrically accurate from both pilot positions. "Decollimation" is any mechanism or process which causes a beam with the minimum possible
ray divergence to diverge or converge from parallelism. Decollimation may be deliberate for systems reasons, or may be caused by many factors, such as
refractive index inhomogeneities, occlusions,
scattering,
deflection,
diffraction,
reflection, and
refraction. Decollimation must be accounted for to fully treat many systems such as
radio,
radar,
sonar, and
optical communications. == See also ==