This page is provided both for general background information on the need for accurate focusing, as well as to provide actionable tips on how to reliably achieve sharp focus. It is a general discussion not aimed at any particular camera brand or lens.
For examples of focus error issues, please see Focus Accuracy at diglloyd.com.
Some photographers still believe that focusing by the distance scale on the lens is sufficient to extract top results if one simply stops down to f/8 or f/11. Experienced digital shooters know that such an approach is inadequate with today’s 10+ megapixel cameras (or even 4-megapixel cameras, to a reduced degree). Stopping down to f/8 from f/2 delivers 4X the depth of field (in theory). If the depth of field is 1 foot at f/2, then it’s only 4 feet at f/8, and with real lenses theoretical and actual depth of field are two different animals. Depth of field does not mean that contrast remains uniform throughout that zone, or that aberrations are all controlled (though stopping down reduces some optical aberrations).
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