Final answer:
Chromatic aberration is caused by a lens's varying index of refraction based on light wavelength, resulting in a dispersion of colors. It can be reduced with an achromatic doublet made of different types of glass. Coma and spherical aberration are other forms of image distortion in optical systems.
Step-by-step explanation:
Aberrations in optical systems are distortions in images caused by various reasons associated with the lens or mirror's size, material, thickness, and position of the object. One of the most common types of aberration is chromatic aberration, which is due to the dependence of a lens's index of refraction on the color (wavelength) of light. This aberration causes different colors of light to have different focal points because different wavelengths are refracted by different amounts. Chromatic aberration can be reduced by using an achromatic doublet, which is made of a converging lens of crown glass and a diverging lens of flint glass in contact. Other aberrations include coma and spherical aberration. Coma occurs when parts of a lens or mirror do not refract or reflect the image to the same point, often resulting in a pear-shaped image, while spherical aberration is when rays from the outer edges of a lens focus closer to the lens than rays near the axis.