1. An imaging device, comprising: an image data acquisition circuit that determines a plurality of focus positions by repeatedly shifting focus position by a given amount, forms subject images at respective focus positions, and acquires, from the subject images that have been formed, a plurality of image data of a first resolution, or a plurality of image data of a second resolution that is different to the first resolution, and an image combination circuit that generates first image data by combining the plurality of image data of the first resolution, or generates second image data by combining the plurality of image data of the second resolution, wherein when generating the first image data, the image data acquisition circuit acquires image data at a focus position that has been shifted by a first given amount, a plurality of image data at a plurality of focus positions is acquired by repeating this image data acquisition for a first number of repetitions, and after that the image combination circuit generates the first image data, while when generating the second image data, the image data acquisition circuit acquires image data at a focus position that has been shifted by a second given amount that larger than the first given amount, a plurality of image data are acquired by repeating this image data acquisition for a second number of repetitions, and after that the image combination circuit generates the second image data.