VARIABLE FOCAL LENGTH LENS DEVICE AND VARIABLE FOCAL LENGTH LENS CONTROL METHOD

A variable focal length lens device (1) includes: a lens system (3) whose refractive index changes depending on an inputted drive signal (Cf); an objective lens disposed in an optical axis common to the lens system (3); an image detector (4) for detecting an image of a target object through the lens system (3) and the objective lens; a resonance-lock controller (611) for locking the frequency of the drive signal (Cf) to a resonance frequency of the lens system (3); and a resonance-lock operation unit (711) for switching between enabling and suspending of the resonance-lock controller (611). 本发明的可变焦距透镜装置(1)具有：折射率根据输入的驱动信号(Cf)变化的透镜系统(3)；配置在与透镜系统(3)相同的光轴上的物镜；通过透镜系统(3)和物镜来检测测量对象物的图像的图像检测单元(4)；使驱动信号(Cf)跟随透镜系统(3)的谐振频率的谐振锁定控制单元(611)；以及切换谐振锁定控制单元(611)的动作或停止的谐振锁定操作单元(711)。