Focus control device, endoscope system, and focus control method

An endoscope system comprising:

• a focus control section that controls an imaging optical system that is configured so that an in-focus object plane position is changed when an imaging magnification is changed;
• an image acquisition section that acquires a plurality of images captured through the imaging optical system at a different imaging magnification;
• a change-in-magnification detection section that detects a change in magnification, the change in magnification being at least one of a change in the imaging magnification and a change in size of an object within an image among the plurality of images;
• and
• an image scaling section that subjects the image to an image scaling process based on the change in magnification to acquire a scaled image,
• the focus control section calculating an autofocus (AF) evaluation value that indicates a focus state of the imaging optical system based on the image and the change in magnification, and driving the imaging optical system based on the calculated AF evaluation value to control focus of the imaging optical system, and
• the image scaling section calculating the detected change in magnification that excludes a change in magnification due to the driving of the imaging optical system for focus control as a target change in magnification, and performing the image scaling process based on the target change in magnification to cancel a change in angle of view due to the driving of the imaging optical system for focus control.

A focus control method that controls an imaging optical system that is configured so that an in-focus object plane position is changed when an imaging magnification is changed, the focus control method comprising:

• acquiring a plurality of images captured through the imaging optical system at a different imaging magnification;
• detecting a change in magnification that is at least one of a change in the imaging magnification and a change in size of an object within an image among the plurality of images;
• subjecting the image to an image scaling process based on the change in magnification to acquire a scaled image;
• calculating an autofocus (AF) evaluation value that indicates a focus state of the imaging optical system based on the acquired image and the change in magnification, and driving the imaging optical system based on the calculated AF evaluation value to control focus of the imaging optical system;
• and
• calculating the detected change in magnification that excludes a change in magnification due to the driving of the imaging optical system for focus control as a target change in magnification, and performing the image scaling process based on the target change in magnification to cancel a change in angle of view due to the driving of the imaging optical system for focus control.