AmbientMike wrote:
If you focus with live view, simply focus at shooting aperture and you\'re in focus. Oof is oof and if you get that from focus shift, you get it from focus shift, and you will get oof images. Focus shift gets worse as you stop down. dof doesn\'t cover it.
In practice, focus shift doesn\'t keep getting worse as you stop down. In a lens with pronounced focus shift, the effect is most noticeable when stopping down slightly from the maximum aperture. You would be hard pressed to identify such focus shift if the lens were stopped down to, say, f/16.
Something else to realize is that people often speak of focus shift as a broad-spectrum phenomenon that requires shooting stopped down from the fastest aperture in order to observe it, but that need not be so. That is, the degree of focus shift in a lens may not be the same at all wavelengths of light. When focus shift is dependent on wavelength rather than f-number, we usually perceive that as longitudinal/axial chromatic aberration. So in practice, these phenomena generally do not exist on their own but are simultaneously present in a given lens with under- or overcorrected spherical aberration. Sometimes we call this \"spherochromatism\"--the observation of spurious color because incident rays of different wavelengths do not converge at the same point, due to spherical aberration and dispersion.
Mar 11, 2011 at 01:57 PM
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