What defect in a lens causes straight lines to appear curved?

Distortion is a defect in a lens that causes straight lines to appear curved. This phenomenon typically occurs due to how the lens bends light as it passes through, leading to a misrepresentation of shapes, especially towards the edges of the lens. In the context of optical systems, distortion can manifest in various ways, including barrel distortion, where lines bulge outwards, and pincushion distortion, where lines pinch inward.

Understanding distortion is crucial in fields like photography and vision correction, where accuracy in image representation is essential. It highlights the importance of optical design and the limitations that may arise in lens fabrication, particularly in scenarios where high-precision optics are required.

The other options—abberation, refraction, and chromatic dispersion—relate to different optical phenomena. Aberration describes imperfections in the image formation that can affect clarity and sharpness, refraction refers to the bending of light as it passes through different media, and chromatic dispersion deals with the wavelength-dependent behavior of light which causes color fringing. However, none of these directly account for the effect of straight lines appearing curved in the same manner that distortion does.