Image detection device and image detection method for reducing focusing recovery time

An image detection method using an image detection device, the image detection device comprising:

• a variable focal length lens, a focal length of the variable focal length lens being periodically changed in response to a drive signal that is periodic;
• an illuminator configured to illuminate a measurement target;
• an image detector configured to detect an image of the measurement target through the variable focal length lens;
• a drive controller configured to output the drive signal to the variable focal length lens;
• and
• a light-emission controller configured to output a light-emission signal to the illuminator, the light-emission signal being in synchronization with the drive signal, wherein
• the light-emission signal is adjusted so that the image of the measurement target to be detected by the image detector is in a focusing state, and the image of the measurement target in the focusing state is detected, and
• oscillation applied from outside to the variable focal length lens is detected by an acceleration sensor attached to a container of the variable focal length lens to acquire oscillation information, a displacement amount caused by the oscillation applied from outside to the variable focal length lens is calculated based on the oscillation information acquired, and an output timing of the light-emission signal is adjusted such that the displacement amount is canceled in the focal length of the variable focal length lens.