Focusing in Landscapes
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10-01-12, 09:51 PM
Join Date: Sep 2010
Location: Hove, actually
DOF is based on a set of assumptions. Only one single distance (with a perfect lens and light behaving differently to the way it in fact does) will reproduce a point as a point; every other distance will give a circle, getting bigger as the subject moves further away from the point you're focused on. DOF depends on the eye accepting a circle as a point; which it will, until the circle reaches a certain size.
Hence DOF tables assume viewing distance, how good your eyes are, and how much you're going to enlarge. Once you step outside these assumptions, the tables lose their value.
If you're looking to produce a print larger than the DOF tables assume, or if your criterion for what is really sharp is more rigorous, if your near vision is more acute in viewing the image, or even if the viewing conditions are better than those assumed, the results at infinity will appear unsharp if you focus on the hyperfocal distance. And that's assuming that the focusing is accurate to start with.
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