Autofocus apparatus, autofocus method, and program

An autofocus method comprising:

• forming an image of an object to be photographed by an optical system and changing the magnification of the image;
• generating a pattern of a plurality of adjacent areas of at least two different luminances, each of a predetermined size, by individually controlling a plurality of micromirrors;
• projecting the pattern onto the object;
• controlling a focus position of the optical system with a desired focusing precision based on a photographed image of the projected pattern, which includes the pattern of the plurality of adjacent areas of at least two luminances, when the predetermined size of the adjacent areas is within a permitted range, by calculating a contrast in the image;
• changing the predetermined size of each adjacent area to fall within the permitted range by
• decreasing the predetermined size when the changing operation increases the magnification of the image, and
• increasing the predetermined size when the changing operation decreases the magnification of the image,
• to render the contrast in the image that includes the pattern of the plurality of adjacent areas of at least two luminances to be sufficient to permit the controlling operation to control the focus position of the optical system with the desired focusing precision;
• and
• forming, by the optical system at the changed magnification, the image of the projected pattern.

A non-transitory computer-readable storage medium that stores a program for execution by an autofocus apparatus, the program product causing the computer to execute a process comprising:

• detecting a magnification of an optical system forming an image of an object, and changing the magnification of the image;
• generating a pattern of a plurality of adjacent areas of at least two different luminances, each of a predetermined size, by individually controlling a plurality of micromirrors,
• the predetermined size of each adjacent area increasing when the optical system increases the magnification of the image without the predetermined size being changed by a calculating operation,
• the predetermined size of each adjacent area decreasing when the optical system decreases the magnification of the image without the predetermined size being changed by the calculating operation;
• generating the pattern by individually controlling a plurality of micromirrors;
• projecting the pattern onto the object;
• controlling a focus position of the optical system with a desired focusing precision based on a photographed image of the projected pattern, which includes the pattern of the plurality of adjacent areas of at least two luminances, when the predetermined size of the adjacent areas is within a permitted range, by calculating a contrast in the image;
• calculating a size of each adjacent area of the pattern to fall within the permitted range by
• decreasing the predetermined size when the changing operation increases the magnification of the image, and
• increasing the predetermined size when the changing operation decreases the magnification of the image,
• to render the contrast in the image that includes the pattern of the plurality of adjacent areas of at least two luminances to be sufficient to permit the controlling operation to control the focus position of the optical system with the desired focusing precision;
• and
• forming, by the optical system at the changed magnification, the image of the projected pattern.