What is the term used for a defect in an image that reduces the resolution produced by a lens?

The term that refers to a defect in an image caused by a lens that negatively impacts the resolution is aberration. Aberration occurs when light rays do not converge at a single point after passing through the lens, leading to various types of distortions in the image. Common forms of aberration include chromatic aberration, where different colors do not focus at the same point, and spherical aberration, where light rays hitting different parts of the lens do not converge at the same point. These defects result in an image appearing less sharp and clear than it should be, thus reducing the effective resolution of the photograph.

In contrast, while distortion refers to the geometric shape of objects being inaccurately represented, and vignetting involves a gradual reduction of brightness toward the corners of the image, neither directly describes a resolution reduction caused by lens defects. Similarly, flare results from bright light sources causing unwanted artifacts but does not pertain specifically to resolution loss from lens defects either.