A lens defect that causes lines at the edges of a lens to be bent more than lines toward the center.

A problem where a lens or mirror in a telescope is not shaped correctly, so the light from the center is focused at a different location than the light from the edges. You should never have to worry about this. This usually shows up only in really cheap telescopes.

Terms referring to (usually small) errors within the primary mirror or lens.

failure of light rays striking all parts of a lens or a mirror with a spherical surface to converge at the same focal setting.

a defect seen in images that is caused by the objective not being exactly shaped (e.g., an objective mirror not being exactly parabolic) so that not all of the light is focussed to the same point.

a optical aberration resulting in a distorted image

a defect caused by grinding that surface of a lens or mirror to a spherical rather that a parabolic shape

Occurs when the converging rays in a concave mirror are not properly focused in one area. To avoid this, parabolic mirrors are used, as they do not have spherical aberration.

An optical aberration in which light from different parts of a mirror or lens is brought to different foci.

A parabolic mirror will focus incoming light to a single point. A spherical mirror will focus incoming light to different points causing stars to no longer appear as nice round points of light. This distortion is called spherical aberration. back to the top

an optical distortion inherent in an optical surface or lens caused by its spherical shape.

This is where an image is distorted because of the fact that the mirror is hemispherical and that a hemispherical mirror does not bring light to a perfect focus. This can be treated in two ways. Firstly by using a paraboloidal mirror rather than a hemispherical one. This works well for narrow fields of view. However for larger angles, the Schmidt plate is more effective. This is commonly used in wide field cameras for example and is commonly combined with a Cassegrain mounting on smaller modern telescope. See also chromatic aberration.

This aberration comes from the fact that a spherical lens or mirror cannot focus all the light rays from a star to a single point. A proper combination of spherical optics or an aspheric optic will minimize this aberration. The corrector lens on the front of a Schmidt-Cassegrain, for example, is an aspheric lens which corrects the aberration from the spherical primary mirror.

The failure of an optical system to focus light of a given wavelength from all parts of the objective to the same point on the optical axis.

Image defect caused by a mismatch in the shapes of the reflecting surfaces of the primary and secondary mirrors. Light from different annular regions on the primary mirror comes to a focus at different distances from the secondary mirror, and there is no one position where all of the light is in focus.

electron optical lens aberration resulting in decreased focal length for rays that are farther from the optical axis.

The axial aberration where rays from the outer periphery of the lens focus closer (or further) from the lens than the rays closer to the axis.

Breach of a point image of a point object by rays refracted from the periphery of a surface to a shorter focal distance than paraxial rays.

A visual disorder reflecting a change in curvature between the center and edge of the pupil. This creates multiple focal points and can cause halos in your vision.

A blurred image caused by the way light passes through spherically shaped (rounded) optics. It is caused by the light at or near the center of the element coming into focus on a separate plane than the light near the edge of the spherical optic.

Lens aberration where rays entering a lens at different positions come to a focus at different points. Often seen when focussing into a thick specimen with oil immersion objectives ( Interactive tutorial).

See Aberration. The magnification power in the center of a lens differs from the magnification possible at the len's edges.

An optical defect in a lens causing the lens to form an image that is not sharp or that is distorted. The larger the lens, the more likely it is to suffer from aberrations. Aberrations are also more common towards the outer portion of a lens.

occurs when a lens is ground perfectly spherical causing light rays to fall at different points on the macula where by a common focus can not be achieved.

blurry defect in optical elements that have a spherical surface, caused by differences in focal length causing light rays to fall on different locations of the macula preventing achievement of a common focus. (Ref: Encarta dictionary)

the non- convergence of rays from one point of focus when passing through a spherical body, produces a scattering effect on the light ray.

is commonly seen after refractive surgery, resulting from the dramatic change in corneal contour at the junction of the ablation zone and peripheral untreated cornea. Spherical aberration is a common cause of nighttime halos and may play a significant role in the loss of contrast sensitivity under low conditions that some patients experience post-operatively.

A lens fault which results in degraded image quality at the film plane. It is caused by light rays passing through the lens from a single point on the optical axis focused at different points according to incident height. Spherical aberration can be reduced by stopping down the lens.

an optical defect in curved mirrors that result in reflected rays not all converging at a principal focus.

The only lens aberration that appears on axis. Results in light rays from the outer portion of the lens focusing either in front of (undercorrected) or behind (overcorrected) the focus point of the rays from the center portion of the lens.

In optics, spherical aberration is an image imperfection that occurs due to the increased refraction of light rays that occurs when rays strike a lens or a reflection of light rays that occurs when rays strike a mirror near its edge, in comparison with those that strike nearer the center. It is often considered to be an imperfection of telescopes and other instruments which makes their focusing less than ideal due to the spherical shape of lenses and mirrors. This is an important effect, as spherical shapes are much easier to produce than aspherical and so most lenses have spherical shapes.