Ultrahigh-performance long-focal-length close-focusing zoom lens for the visible waveband

A long focal length close focusing zoom lens for the visible waveband which rivals the performance of fixed long focal length lenses is described. Particular areas of discussion include, the utilization of anomalous glasses to control secondary color and the choice of focus system configuration to minimize breathing, provide continuous close focusing to macro magnifications and the reduction of the number of large diameter elements required.