Spherical Aberration

Rays emanating from an object point that are incident on a spherical mirror or lens at different distances from the optical axis, after reflection or refraction, either intersect, or appear to intersect, at different positions. Definition:

Diagram:

Ideal situation Real situation

Diagram:

Photo: Positive …. aberration Negative …. aberration zero …. aberration

Correction: Use “stops” so that only nearly paraxial rays (i.e. rays near the optical axis) get through to the lens (or spherical mirror).

Correction: Combine positive and negative lenses in an arrangement so that the …. aberration from one tends to cancel that from the other.

chromatic Aberration

Definition: It results because the index of refraction of a material differs for different wavelengths. Since the focal length of a lens is dependent on the index of refraction of the lens material, focal lengths and image positions differ for different wavelength components of the light used in the optical system.

Definition: is limited only to lenses. Mirrors cannot cause this type of aberration.

Diagram:

Off-axis: lateral

Photo:

Correction: Use multiple refractive elements of opposite powers.

Coma Aberration

Definition: It derives its name from the cometlike appearance of the image of an object point located just off the lens axis.

Diagram:

Photo:

Astigmatism Aberration

Definition: It is an aberration where rays that propagate in two perpendicular planes have different foci. It is an optical aberration in which, instead of rays converging to a single focus, they are caused to focus to two lines at right angles, separated by an interval.

Diagram:

Correction: Correction involves the use of planocylindrical, spherocylindrical, or spherotoric lenses.

Field curvature Aberration

Definition: In general, a plane object at right angles to the axis of an optical system will not give rise to a plane image. Instead, the image would lie on a paraboloid surface known as the Petzval surface.

Diagram:

Photo:

Distortion Aberration

Definition: Angular deviation of the wavefront destroying the linear relation between dimensions in object and image.

Diagram: None Pincushion barrel

Photo: