What is bokeh, and what makes it look different between lenses?
Bokeh describes the quality and character of out-of-focus rendering — not how much blur there is (that's depth of field), but what the blur actually looks like. Two lenses can produce the identical amount of background blur at the same focal length, aperture and distance, and still look completely different, because bokeh is shaped by the lens's own optical design, not by the depth-of-field formula at all.
Why Depth of Field and Bokeh Are Genuinely Separate Things
Depth of field, computed from sensor size, focal length, aperture and distance, tells you the size and extent of the out-of-focus region. Bokeh describes its texture — smooth and creamy, busy and nervous, or ringed with visible outlines — which comes from factors the depth-of-field formula doesn't touch: the aperture diaphragm's blade shape and count (more blades, especially rounded ones, generally produce smoother out-of-focus highlights than a hard-edged five- or six-blade design), spherical and chromatic aberration correction, and specific lens-element choices some manufacturers make deliberately for rendering character rather than pure sharpness.
Why Two f/1.4 Lenses Can Look So Different
A vintage manual-focus 50mm f/1.4 and a modern computer-optimized 50mm f/1.4 can produce nearly identical depth of field at the same distance, while rendering their out-of-focus backgrounds in visibly different ways — one smoother and dreamier, the other more clinical and neutral, or showing visible 'onion ring' texture from certain aspherical element manufacturing methods. This is exactly why some photographers choose a specific lens deliberately for its bokeh character, independent of its raw depth-of-field or sharpness specifications.
Work out how much depth of field (the extent of the blur, not its character) your own setup produces in the DoF & Hyperfocal Calculator.
Frequently Asked Questions
Does a rounder aperture diaphragm always produce better bokeh?
It generally produces smoother, more circular out-of-focus highlights, especially when stopped down slightly from wide open, but 'better' bokeh is genuinely subjective beyond that — some photographers specifically prefer a busier or more geometric rendering style that a rounder diaphragm would smooth away.
Can I predict a lens's bokeh from its specifications alone?
Only partially — aperture blade count and shape are listed specs that give a rough clue, but the fuller character of a lens's bokeh depends on optical design choices that aren't fully captured by any single published number, which is why sample images and hands-on testing remain the most reliable way to judge it.