A vision system includes a variable focal length (VFL) lens system, a light source, an exposure time controller and a camera. The VFL lens system includes a tunable acoustic gradient index of refraction (TAG) lens that is controlled to provide a nominally sinusoidal modulation of a focus position. The light source includes a continuous illumination source connected to a source driver that drives the continuous illumination source based on a quasi-sinusoidal periodic drive function to provide corresponding quasi-sinusoidal periodic intensity modulated light. The camera provides a workpiece image based on an image exposure that inputs workpiece image light that arises from illuminating the workpiece with the quasi-sinusoidal periodic intensity modulated light. Utilization of the quasi-sinusoidal periodic intensity modulated light in combination with the nominally sinusoidal focus position modulation results in uniform image exposures and other advantages (e.g., by avoiding over-exposure at the focus extremes of the TAG lens, etc.).