Fiveable
Fiveable
Fiveable
Fiveable

🔬Modern Optics

🔬modern optics review

14.2 Optical aberrations and their correction

3 min readLast Updated on July 22, 2024

Optical aberrations can wreak havoc on image quality. From spherical aberration to chromatic fringing, these pesky distortions blur details and reduce contrast. But fear not! There are ways to fight back.

Clever lens designs and adaptive optics can correct many aberrations. By combining different materials and shapes, or using deformable mirrors, we can sharpen images and boost performance. Evaluating corrections helps push optical systems to their limits.

Types and Causes of Optical Aberrations

Types of optical aberrations

Top images from around the web for Types of optical aberrations
Top images from around the web for Types of optical aberrations
  • Spherical aberration occurs when light rays passing through the edges of a spherical lens or mirror focus at a different point than rays passing near the center resulting in a blurred image and reduced contrast
  • Coma is an off-axis aberration that occurs when light from an off-axis point source is focused at different positions depending on the zone of the lens or mirror it passes through causing a comet-shaped blur in the image with the "tail" pointing away from the optical axis
  • Astigmatism occurs when a lens or mirror has different focal lengths in two perpendicular planes resulting in an image that is sharp along one axis but blurred along the other
  • Chromatic aberration caused by the wavelength-dependent refractive index of optical materials has two main types:
    • Axial (longitudinal) chromatic aberration where different wavelengths focus at different distances along the optical axis
    • Lateral (transverse) chromatic aberration where different wavelengths focus at different positions in the image plane
  • Chromatic aberration results in color fringing and reduced image sharpness

Causes and effects of aberrations

  • Causes of aberrations include:
    • Spherical surfaces in lenses and mirrors
    • Misalignment of optical components
    • Wavelength-dependent properties of optical materials (dispersion)
  • Effects of aberrations on image quality include:
    • Reduced sharpness and contrast
    • Blurring and distortion (coma, astigmatism)
    • Color fringing and chromatic errors (chromatic aberration)
    • Loss of resolution and detail

Correction Methods and System Performance

Methods for aberration correction

  • Aspheric surfaces are non-spherical lens or mirror surfaces designed to minimize spherical aberration and can be used in combination with spherical surfaces to balance aberrations
  • Achromatic doublets combine two lenses with different dispersion properties (crown and flint glass) to minimize chromatic aberration by ensuring that two or more wavelengths focus at the same point
  • Adaptive optics actively correct aberrations using deformable mirrors or liquid crystal spatial light modulators:
    1. Wavefront sensing measures the aberrations
    2. The corrective element is adjusted in real-time to compensate
    • Commonly used in astronomy and high-resolution imaging systems (telescopes, microscopes)

Evaluation of aberration correction

  • Wavefront analysis measures the deviation of the actual wavefront from the ideal wavefront:
    • Quantified using Zernike polynomials or other basis functions
    • Provides a comprehensive assessment of the system's aberrations
  • Modulation transfer function (MTF) describes the contrast transfer of an optical system as a function of spatial frequency:
    • Indicates the system's ability to resolve fine details and maintain contrast
    • Can be measured experimentally or calculated from the system's aberrations
  • Strehl ratio is the ratio of the peak intensity of the aberrated point spread function (PSF) to that of the ideal, diffraction-limited PSF:
    • Provides a single-value measure of the system's overall image quality
    • A Strehl ratio of 1 indicates a perfect, diffraction-limited system, while lower values indicate the presence of aberrations


© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.