Focus shift and how to mitigate it are discussed in detail in Making Sharp Images.
The 36-megapixel Nikon D800E was used as shown below. The test scene measures 15" (38 cm) across, so this corresponds to a tight “head shot” portrait.
Focus was on the doll’s eyes (Miss Checkerboard at center), with the ruler as a reference point for observing the amount of focus shift. The doll’s eyes correspond to the ~ “14.5” mark on the ruler.
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