What does achromatic mean in relation to lenses?

Achromatic, in relation to lenses, refers to the property of refracting light without introducing color distortion. This characteristic is particularly important in optical systems because different wavelengths of light are usually refracted to different extents, which can cause chromatic aberration—meaning that colors do not focus at the same point. An achromatic lens uses specific curvature and materials to minimize this distortion, allowing for a clearer and more accurate image by effectively bringing multiple colors to the same focal point.

The other options talk about attributes that do not pertain to the definition of achromatic. For example, the idea of creating vibrant colors or producing a rainbow effect relates more to the manipulation or dispersion of color rather than eliminating distortion. Similarly, the ability to darken light significantly does not connect with the concept of color correction, which is central to the definition of achromatic lenses.