A focus tunable optical system includes a lens assembly. The lens assembly includes: focus tunable lenses (FTLs) coaxially disposed along an optical axis, each FTL contributing to an optical power of the lens assembly; and a controller configured to control the optical power of the lens assembly by applying to each FTL a respective control signal, thereby generating a periodic optical response of the respective FTL. The optical response of each FTL is substantially different from the optical response of any other FTL of the plurality of FTLs.