Discrete zoom systems are commonly used as laser beam expanders and infrared zoom lenses. The reason to design a
discrete zoom lens is that they are often a desirable compromise between fixed-focal length lenses and continuous zoom
lenses, offering many advantages to imaging systems of all types. They have the advantage over continuous zoom systems
for containing fewer elements, thus reducing the weight of the system, and having one mechanical motion instead of two.
In literature there is little information on the first order parameters and starting requirements for discrete systems. This
work derives the first order equations for two different discrete zoom systems. The equations are derived from the
requirements of first order parameters which define the starting group focal lengths. The two design configurations studied
are: one zoom group flipping in and out of the system; one zoom group moving laterally along the optical axis. This work
analyzes the first order equations for both configurations and discusses the starting point for the designs taking into
consideration system limitations. Final designs for both configurations are then compared over several parameters: group
focal lengths, lens diameters, overall length, number of elements, materials, and performance.