The simplest telephoto designs could consist of one element in each group, but in practice, more than one element is used in each group to correct for various aberrations.
Sharpness is often the first casualty, and barrel and pin-cushion distortions often appear at the wide-angle and telephoto ends of the zoom range respectively.
Each format offers advantages and disadvantages which become more or less important in different usage settings (e.g. studio vs sport, indoor vs outdoor, wide angle vs telephoto).
