Benefit of Achromatic Doublets
An achromatic lens is far superior to a simple lens for multi-color "white light" imaging. The two elements composing an achromatic lens (literally, "a lens with no color") are paired together for their ability to correct the color separation inherent in glass. Having eliminated the problematic chromatic aberrations, an achromatic lens becomes the most cost-efficient means for good polychromatic illumination and imaging. Refer to Figure 8 for an illustration of this concept.