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Message: <blockquote data-quote="nirofo" data-source="post: 1833023" data-attributes="member: 1854">You miss the point, depth of field becomes less and less the closer you get to the subject; it can reach a point, especially on long zoom lenses, where it is almost non existent.  This depends on what apperture you are using, I assume you are using a wide aperture at the 500mm end of the lens; if you are, focussing becomes super critical at close distance.  While it might appear to be out of focus at the point you intended to be sharp, it could in fact be in focus elsewhere on the subject.  As mentioned previously, focussing on the Nikon D300 is very fast and it can have refocussed on another point in the picture if it is the nearest focus point, you may not be aware this has happened.  Try focussing manually on a fixed point, don't use the lens wide open, stop it down at least half a stop, Sigma 150-500 zooms are crap wide open anyway! nirofo.</blockquote>