What Is an Optical Axis?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 14 September 2019
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An optical axis is a line running through a point of rotational symmetry in a lens or crystal. This may also be the site of the mechanical axis, although not necessarily. Characteristics of optics elements like the locations of their axes have an important impact on their performance and can determine which product is most appropriate for a given application. In production of lenses, technicians typically run some tests to make sure finished lenses, crystals, and other elements meet technical specifications.

In something like a dome magnifier, the optical axis runs from front to back in the middle of the dome. The magnifier’s properties are symmetrical around this axis; if it is rotated, the magnification will remain the same, as will any distortion and errors near the edges of the lens. For other types of optics, the optical axis may be offset for specific purposes. Calibration can be more difficult with offset optics, because they have to be positioned very precisely in order to work properly.

Some equipment may have more than one optical axis. This can be seen with equipment like biaxial crystals, which have, as the name implies, two axes. They can be rotated around either one for symmetrical performance. The number of axes can depend on the material an element is made from, and the formation of the lattice inside. Crystals are capable of extremely complex internal structures that can permit the creation of multiple axes and other distinctive properties.


Mechanical testing can be used to determine the location of an optical axis. Technicians may use such equipment when they test finished optics products, to make sure they will work properly. This can also be useful for calibration purposes, particularly with offset lenses that require careful handling. Usually the equipment can check for several different optical properties and generate a complete report on the material being tested.

Lens grinders used to make lenses for optics can be set with a variety of parameters to determine their specifications. Synthetic crystals grown in controlled conditions can also be manipulated to create a specific optical axis and other properties. In both cases, there are low tolerances for error; with corrective lenses, for example, small aberrations in the lens can cause vision problems like blurring and eye strain for the wearer. Technicians monitor the environment and follow strict production protocols to reduce the risk of errors during production of optical components.


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