In optics, spherical aberration (SA) is a type of aberration found in optical systems that have elements with spherical surfaces. This phenomenon commonly affects lenses and curved mirrors, as these components are often shaped in a spherical manner for ease of manufacturing. Light rays that strike a spherical surface off-centre are refracted or reflected more or less than those that strike close to the centre. This deviation reduces the quality of images produced by optical systems. The effect of spherical aberration was first identified in the 11th century by Ibn al-Haytham who discussed it in his work Kitāb al-Manāẓir.
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👉 Spherical aberration in the context of Curved mirror
A curved mirror is a mirror with a curved reflecting surface. The surface may be either convex (bulging outward) or concave (recessed inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. The most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems, like spherical lenses, suffer from spherical aberration. Distorting mirrors are used for entertainment. They have convex and concave regions that produce deliberately distorted images. They also provide highly magnified or highly diminished (smaller) images when the object is placed at certain distances. Convex mirrors are often used for security and safety in shops and parking lots.
In this Dossier
- ⭐ Core Definition: Spherical aberration
- 👉 Spherical aberration in the context of Curved mirror
- Spherical aberration in the context of Simple lens
- Spherical aberration in the context of Great Observatories program
- Spherical aberration in the context of Barrel distortion
- Spherical aberration in the context of STS-61
Spherical aberration in the context of Simple lens
In optics, a simple lens or singlet lens is a lens consisting of a single simple element. Typical examples include a magnifying glass or a lens in a pair of simple reading glasses.
Simple lenses are prone to aberrations, especially chromatic aberration. They cannot be used for precise imaging and make poor camera lenses. They are commonly used for laser applications, however, where the beams are both monochromatic (minimizing chromatic aberration) and narrow (minimizing spherical aberration).
Spherical aberration in the context of Great Observatories program
NASA's series of Great Observatories satellites are four large, powerful space-based astronomical telescopes launched between 1990 and 2003. They were built with different technology to examine specific wavelength/energy regions of the electromagnetic spectrum: gamma rays, X-rays, visible and ultraviolet light, and infrared light.
The Hubble Space Telescope (HST) primarily observes visible light and near-ultraviolet. It was launched in 1990 aboard the Space Shuttle Discovery during STS-31, but its main mirror had been ground incorrectly, resulting in spherical aberration that compromised the telescope's capabilities. The optics were corrected to their intended quality by the STS-61 servicing mission in 1993. In 1997, the STS-82 servicing mission added capability in the near-infrared range, and in 2009 the STS-125 servicing mission refurbished the telescope and extended its projected service life. It remains in active operation as of October 2024.
Spherical aberration in the context of Barrel distortion
In geometric optics, distortion is a deviation from rectilinear projection; a projection in which straight lines in a scene remain straight in an image. It is a form of optical aberration that may be distinguished from other aberrations such as spherical aberration, coma, chromatic aberration, field curvature, and astigmatism in a sense that these impact the image sharpness without changing an object shape or structure in the image (e.g., a straight line in an object is still a straight line in the image although the image sharpness may be degraded by the mentioned aberrations) while distortion can change the object structure in the image (so named as distortion).
Spherical aberration in the context of STS-61
STS-61 was NASA's first Hubble Space Telescope servicing mission, and the fifth flight of the Space Shuttle Endeavour. The mission launched on December 2, 1993, from Kennedy Space Center (KSC) in Florida. The mission restored the spaceborne observatory's vision (marred by spherical aberration in its mirror) with the installation of a new main camera and a corrective optics package (COSTAR). This correction occurred more than three and a half years after the Hubble was launched aboard STS-31 in April 1990. The flight also brought instrument upgrades and new solar arrays to the telescope. With its very heavy workload, the STS-61 mission was one of the most complex in the Shuttle's history.
STS-61 lasted almost 11 days, and crew members made five spacewalks (extravehicular activities (EVAs)), an all-time record; even the re-positioning of Intelsat VI on STS-49 in May 1992 required only four. The flight plan allowed for two additional EVAs, which could have raised the total number to seven; the final two contingency EVAs were not made. In order to complete the mission without too much fatigue, the five EVAs were shared between two pairs of different astronauts alternating their shifts. During the flight, mission specialist Jeffrey A. Hoffman also spun a dreidel for the holiday of Hanukkah to a live audience watching via satellite.