What is Spherical Aberration?

What is Spherical Aberration?

Spherical aberration is an optical phenomenon that occurs when light rays passing through a lens or reflecting off a curved mirror do not converge to a single focal point. Instead, the rays focus at different points depending on their distance from the optical axis, resulting in a blurred or distorted image.

This aberration is caused by the spherical shape of lenses or mirrors, as opposed to the ideal parabolic or elliptical shapes that would bring all incoming light rays to a single focal point. Spherical aberration can occur in various optical systems, such as camera lenses, telescopes, microscopes, and eyeglasses.

Types of spherical aberration

There are two types of spherical aberration:

Positive Spherical Aberration

This occurs when light rays passing through the outer portions of a lens or mirror converge to a focal point closer to the lens than those passing through the center. It results in a blurred image with a “halo” effect around bright objects.

Negative Spherical Aberration

In this case, the outer rays converge to a focal point farther away from the lens or mirror than the central rays. This leads to a blurred image with a larger, softer appearance.

To minimize or eliminate spherical aberration, optical designers often use combinations of lenses with different curvatures, such as compound lenses, or incorporate corrective elements in the design. Additionally, aspheric lenses or mirrors, which deviate from a simple spherical shape, can be employed to reduce spherical aberration and improve the overall optical performance of the system.

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