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Depth of field is also NOT directly related to background blur. Depth of field equations tell you over what range of distances objects will appear to be acceptably sharp (or at least not unacceptably unsharp). It tells you nothing about how much blur there will be of objects well outside the depth of field. That's governed by different physical parameters and determined using totally different equations, and it's something I intend to address in a future article.
donc la valeur de la profondeur de champ ne donne pas directement la quantité et donc encore moins le rendu du flou d'arrière plan.
Citation:
If the background is far enough away (well outside the depth of field) and the subject if fairly close (well inside the hyperfocal distance) the degree of blurring is related to the absolute physical size of the lens aperture. For a 56mm f5.6 lens that would be 10mm and for an 85mm f5.6 lens it would be 85/5.6 = 15mm. So you'd expect the far distant background blur of the 85/5.6 to be about 50% more than that of the 56/5.6, and, in fact, it is!
le flou d'arrière plan/bokeh d'un objectif utilisé en portrait (avec un arrière plan éloigné) est donc donné par le rapport focale/ouverture. Plus le rapport est grand (plus l'ouverture physique est grande), plus le flou est grand.
