In photography, Spherical Aberration is a defect in camera lenses that causes light from different points on the object being photographed to come to a focus at different points. Spherical Aberration causes softness of the image and some F‑stop numbers to be incorrect. Spherical Aberration can be corrected with lens elements made of higher quality glass.
There are two kinds of lens aberrations: chromatic (the inability to focus different wavelengths of color at the same spot) and monochromatic (when lenses are unable to focus a single color of light). One of the most prevalent monochromatic subtypes is spherical aberration.
What is spherical aberration?
Spherical aberration is a lens aberration caused by the focusing of all incoming light rays after passing through a spherical surface. Light rays that pass near the lens’s horizontal axis are refracted less than rays closer to the edge or “periphery” of the lens, and they subsequently appear at different locations across the optical axis.In other words, after passing through the lens, incoming light’s parallel light rays do not converge at the same spot. Because of this, spherical aberration can degrade picture quality and clarity, making it difficult to capture clear photos. An example of spherical aberration is shown below:
How does spherical aberration occur?
Spherical aberration occurs when light rays pass through spherical lens and focus at various locations on a camera’s sensor. It’s a form of monochromatic aberration, which is defined as an optical flaw caused by a lens concentrating on just one color of illumination.
Manufacturers frequently use spherical surfaces for lenses and curved mirrors because it is simpler and less expensive to manufacture spherical surfaces than aspherical or gradient-index ones.
Here’s how spherical aberration occurs in technical terms:
- Spherical surfaces that pass light near the horizontal axis (paraxial rays) refract less than those that pass closer to the edge (peripheral rays). As a consequence, parallel light rays never converge as they travel across the optical axis.
- The most significant difference is that when a wavefront is spherical aberrated, peripheral rays focus closer to the lens than paraxial rays do. The distance between where the two types of rays end up focusing is a method to assess the severity of spherical aberration in a system.
Keeping your camera lens clean can help avoid aberration. You might also notice color fringing and sharpness issues if your lens has aberration issues.
Spherical aberration is a wavelength-independent type of aberration. That means it occurs constantly, regardless of the color or wavelength of light passing through it. Spherical aberration affects only flat wavefronts and the condition continues to hold true no matter how far from the lens you’re looking. In short, spherical aberration affects incoming light rays. As a photographer it is important to be aware of this phenomenon and how it can affect the final image.