Seidel aberrations refer to a set of monochromatic aberrations in optical systems, named after the German mathematician and physicist Ludwig von Seidel. These aberrations describe deviations from ideal imaging conditions in optical systems and can affect the quality and precision of images formed by lenses or mirrors.
The Seidel aberrations include the following five primary aberrations:
Spherical aberration: This aberration occurs when parallel rays of light incident on different zones of a lens or mirror converge at different points, resulting in a blurred or defocused image. Spherical aberration is caused by the spherical shape of lens surfaces.
Coma: Coma causes off-axis point sources to appear distorted, resembling comet-like shapes. It occurs when rays entering the lens or mirror at an angle do not converge to a single point.
Astigmatism: Astigmatism results in different focal lengths for rays in different meridians (planes perpendicular to the optical axis). This leads to distorted images, especially away from the optical axis.
Petzval field curvature: This aberration is related to the curvature of the image field. In systems with Petzval field curvature, the image does not lie on a flat surface, which can affect the focus across the entire field of view.
Distortion: Distortion causes a variation in magnification with distance from the optical axis. There are two types of distortion: barrel distortion (magnification decreases with distance from the axis) and pincushion distortion (magnification increases with distance from the axis).
These Seidel aberrations collectively describe the imperfections in imaging systems and are crucial considerations in optical design. Optical designers use various techniques, such as aspheric lens surfaces and lens combinations, to minimize or correct these aberrations and achieve high-quality imaging performance.