EXCERPT page containing first few paragraphs. 2019-05-26 11:24:52
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This page shows focus shift of the Nikon AF-S NIKKOR 70-200mm f/2.8E FL ED VR at 200mm at a reproduction ratio of roughly 1:7.
The ratio of 1:7 was chosen because this is a tight head shot distance, thus making that reproduction ratio highly relevant to real world shooting. Sharp eyes are critical in a portrait, hence focus shift is a key performance attribute.
Nikon AF and focus shift
There is a major contextual consideration as to whether the focus shift matters or not: evidence suggests that some cameras such as the Nikon D810 with the latest firmware in fact modify the autofocus system to compensate for focus shift. Thus if the shooting aperture is set to f/5.6, the camera optimizes focus for an assumed shooting aperture of f/5.6, which means that through the viewfinder the image could appear slightly soft!
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