| Depth of focus doesn’t present itself in the final image. It’s generally irrelevant to practical photography from the point of vide of the photographer (as opposed to the camera designer or lens manufacturer). The first quote is talking about depth of field (i.e. how quickly focus falls off from the plane of perfect focus). FWIW, here is what Claude has to say: >> Is depth of focus, as opposed to depth of field, generally relevant to practical photography? > Not really, no. Depth of focus and depth of field are related but distinct concepts, and for practical photography, depth of field is what matters almost all the time. > Depth of field refers to the zone in front of the camera where subjects appear acceptably sharp. This is what photographers think about constantly: choosing apertures to blur backgrounds in portraits, stopping down for landscapes to keep everything sharp, figuring out hyperfocal distance, etc. > Depth of focus refers to the tolerance zone behind the lens, at the image plane (the sensor or film), within which the image remains acceptably sharp. It tells you how precisely the sensor needs to be positioned relative to the lens for focus to be maintained. > For the overwhelming majority of photographers, depth of focus is invisible because it's a manufacturing and engineering concern, not a shooting concern. Camera makers deal with it when designing bodies and ensuring sensor flatness, lens mount tolerances, and autofocus calibration. You encounter it indirectly if you ever need to calibrate autofocus micro-adjustments, shim a lens, or diagnose back/front focus issues, but you don't actively manipulate it while composing a shot. |