Aberrations in Optical Images: Chromatic and Spherical Imperfections

Aberrations in Optical Images

BSc Hons Physics Presentation

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• Introduction to Aberrations
• Chromatic Aberration
• Spherical Aberration
• Correction in Optical Systems
• Conclusion

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1

Introduction to Aberrations

Understanding image distortions in optical systems

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• Aberration causes images to be blurred, distorted, or with color fringing
• Departure from paraxial optics: light from one object point fails to converge to a single image point
• Occurs due to limitations of simple optical theory, not flaws in elements
• Results in non-sharp images requiring correction in optical instruments

• Ideal paraxial rays focus sharply
• Aberrated rays spread out causing blur
• Analyzed using geometrical optics

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2

Chromatic Aberration

Failure to focus all colors to the same point

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• Lens fails to focus all wavelengths to the same point
• Due to dispersion: refractive index decreases with increasing wavelength
• Focal length varies by color, causing different focus distances or magnifications
• Appears as color fringes or purple fringing at high-contrast edges

• Shorter wavelengths (blue) refract more, shorter focal length
• Longer wavelengths (red) focus farther
• Results in colored blur at image plane

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3

Spherical Aberration

Imperfections in spherical lenses and mirrors

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• Common in spherical lenses and curved mirrors due to manufacturing ease
• Peripheral rays refract/reflect more than central rays
• Reduces image quality; first noted by Ibn al-Haytham (11th century) in Kitāb al-Manāẓir
• Leads to blurred images as rays don't converge at one point

• Paraxial rays (near axis) focus at ideal point
• Marginal rays (outer) converge sooner
• Corrected using aspheric surfaces or stops

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• Use achromatic doublets (crown + flint glass) to minimize chromatic aberration
• Aspheric surfaces or parabolic mirrors reduce spherical aberration
• Aperture stops limit off-axis rays
• Geometrical optics and ray-tracing for design optimization
• Essential for high-quality imaging systems

Optical aberrations blur and distort images but can be corrected using advanced lens designs and materials. Essential knowledge for physics and optics.

Thank you! Questions?

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