Lens aberrations
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Spherical and chromatic aberrations.
Spherical aberration (edge rays focus differently) and chromatic aberration (colours focus at different points) blur images. Cured by combining lenses (achromatic doublets) or aspheric surfaces.
Cheap lenses show colour fringes.
Mirrors don't suffer chromatic aberration.
In more detail
Lens aberrations are imperfections in image formation, including spherical aberration, chromatic aberration and distortion. They arise from the shape of lenses and the dispersion of glass.
Real-world uses
- Camera lenses use multiple elements to reduce aberrations.
- Telescopes use special glass or mirrors to reduce chromatic aberration.
- Lens designers correct chromatic aberration by combining glasses with different dispersion to bring all colours to one focus.
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Frequently asked questions
What is chromatic aberration?
Different colours focus at different points because the refractive index depends on wavelength.
How is it corrected?
By combining lenses of different glass types, such as achromatic doublets.
What is spherical aberration?
Light rays near the edge of a lens focus at a slightly different point from those near the centre, which blurs the image.
Related topics in Optics
Lens maker's formula · Power of a lens · Combination of lenses · Human eye · Defects of vision · Simple microscope