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Which image problems can lens designers reduce by combining several lens elements?

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Diagram showing the negative-positive photographic process: a scene is captured on film in a camera, developed into a negative, projected onto paper with an enlarger, and developed again to produce a positive print. — technology of photography Figure 1: Sequence of negative–positive process, from the photographing of the original scene to enlarged print (see text).

Lens designers combine multiple lens elements into a compound lens system to correct various optical imperfections known as aberrations, which prevent a single lens from focusing light into a perfect point. By using elements of different materials and shapes, designers can reduce the following image problems:1

Chromatic aberration: Occurs when different colors of light focus at different planes or scales; it is corrected by combining lenses of different refractive and dispersive properties.213
Spherical aberration: Happens when the outer parts of a lens focus light differently than the center, resulting in unsharp images at large apertures.24
Curvature of field: A condition where the sharpest image is formed on a curved surface rather than a flat plane.2
Astigmatism: Occurs when the lens fails to focus image lines running in different directions on the same plane.2
Coma: Causes image points near the edges of the frame to appear as irregular, unsharp shapes.2
Distortion: Results in straight lines near the edges of the image bowing inward or outward.2