The effects of dispersion are called chromatic aberration.

1. Light refracts colors according to their wavelength. White light has a tendency to break into a spectrum as it’s medium changes. This divergence is called dispersion. We want glass that has a low tendency to do this. Hence, glass makers have invented low-dispersion (LD) glass, extra-low dispersion (ED) glass, Extraordinary-low dispersion (ELD) glass and ultra-low dispersion (ULD) glass.

2. The low dispersion glass types are often found in telephoto lenses where fast f/stops are desired. The effects of dispersion are called chromatic aberration. Early solutions for chromatic aberrations included incorporation of radioactive materials into optical glass.

3. “L” Series Lenses About their “L” lenses, Canon says "these lenses use special optical technologies [such as] Ultra-low Dispersion UD glass, Super Low Dispersion glass, Fluorite elements, and Aspherical elements to truly push the optical envelope." The truth is long lenses may use ULD and Fluorite glass, but wide angles and lenses of shorter than 200mm do not. Wide angles may use aspheric lens elements but not LD glass types. Long lenses do not use aspheric lenses. EF 17-40mm f/4 L USM EF 14mm f/2.8 L USM EF 70-200 f/2.8 L IS USM

4. Aspheric Lenses Most lens elements are ground using a single focal point. An aspheric lens is ground around multiple focal points. Typically, you find greater or even negative curvature on the periphery of the lens. Spherical Lens Element Aspherical Lens Element The reason for incorporating this level of technology is to produce smaller and lighter lenses.