A variable focal length lens system, comprising: a VFL lens; a VFL lens controller that controls the VFL lens to periodically modulate an optical power of the VFL lens over a range of optical powers at an operating frequency; an objective lens that inputs workpiece light arising from a workpiece surface during a workpiece imaging mode and transmits the workpiece light along an imaging optical path that passes through the VFL lens; and a camera that receives the workpiece light transmitted by the VFL lens along the imaging optical path during the workpiece imaging mode and provides a corresponding workpiece image exposure; characterized in that the VFL lens system further comprises: an optical power monitoring configuration comprising a monitoring beam generator comprising a light source and a beam pattern element that inputs light from the light source and outputs a monitored beam pattern, wherein: the optical power monitoring configuration transmits the monitored beam pattern along at least a portion of the imaging optical path to travel through the VFL lens to the camera during an optical power monitoring mode; the camera provides at least a first monitoring image exposure including the monitored beam pattern during at least a first phase timing of the periodic modulation of the VFL lens during the optical power monitoring mode; a dimension of the monitored beam pattern in the first monitoring image exposure is related to an optical power of the VFL lens during the first phase timing; the camera further provides at least a second monitoring image exposure including the monitored beam pattern during a second phase timing of the periodic modulation of the VFL lens during the optical power monitoring mode; and a dimension of the monitored beam pattern in the second monitoring image exposure is related to an optical power of the VFL lens during the second phase timing. a VFL lens; a VFL lens controller that controls the VFL lens to periodically modulate an optical power of the VFL lens over a range of optical powers at an operating frequency; an objective lens that inputs workpiece light arising from a workpiece surface during a workpiece imaging mode and transmits the workpiece light along an imaging optical path that passes through the VFL lens; and a camera that receives the workpiece light transmitted by the VFL lens along the imaging optical path during the workpiece imaging mode and provides a corresponding workpiece image exposure; characterized in that the VFL lens system further comprises: an optical power monitoring configuration comprising a monitoring beam generator comprising a light source and a beam pattern element that inputs light from the light source and outputs a monitored beam pattern, wherein: the optical power monitoring configuration transmits the monitored beam pattern along at least a portion of the imaging optical path to travel through the VFL lens to the camera during an optical power monitoring mode; the camera provides at least a first monitoring image exposure including the monitored beam pattern during at least a first phase timing of the periodic modulation of the VFL lens during the optical power monitoring mode; a dimension of the monitored beam pattern in the first monitoring image exposure is related to an optical power of the VFL lens during the first phase timing; the camera further provides at least a second monitoring image exposure including the monitored beam pattern during a second phase timing of the periodic modulation of the VFL lens during the optical power monitoring mode; and a dimension of the monitored beam pattern in the second monitoring image exposure is related to an optical power of the VFL lens during the second phase timing. an optical power monitoring configuration comprising a monitoring beam generator comprising a light source and a beam pattern element that inputs light from the light source and outputs a monitored beam pattern, wherein: the optical power monitoring configuration transmits the monitored beam pattern along at least a portion of the imaging optical path to travel through the VFL lens to the camera during an optical power monitoring mode; the camera provides at least a first monitoring image exposure including the monitored beam pattern during at least a first phase timing of the periodic modulation of the VFL lens during the optical power monitoring mode; a dimension of the monitored beam pattern in the first monitoring image exposure is related to an optical power of the VFL lens during the first phase timing; the optical power monitoring configuration transmits the monitored beam pattern along at least a portion of the imaging optical path to travel through the VFL lens to the camera during an optical power monitoring mode; the camera provides at least a first monitoring image exposure including the monitored beam pattern during at least a first phase timing of the periodic modulation of the VFL lens during the optical power monitoring mode; a dimension of the monitored beam pattern in the first monitoring image exposure is related to an optical power of the VFL lens during the first phase timing; the camera further provides at least a second monitoring image exposure including the monitored beam pattern during a second phase timing of the periodic modulation of the VFL lens during the optical power monitoring mode; and a dimension of the monitored beam pattern in the second monitoring image exposure is related to an optical power of the VFL lens during the second phase timing.