Which portrait focal length gives the shallowest depth of field?
Among common portrait focal lengths, longer wins: at a comparable framing and the same f-number, 135mm produces shallower depth of field than 85mm, which produces shallower depth of field than 50mm. At full-frame f/1.4-equivalent apertures and portrait-appropriate distances, 85mm's total depth of field at 3 meters (roughly 9.8cm at f/1.4) is already thinner than 50mm's at a closer, framing-matched distance — and 135mm at its own matched distance thins the sharp zone further still.
Why Longer Focal Length Wins This Comparison
Depth of field narrows as real focal length increases at a fixed subject distance, and portrait focal lengths are typically compared at their own natural working distance for a given framing — a headshot needs the camera closer at 50mm than at 135mm to fill the frame the same way. Both effects push in the same direction: the longer lens, working from further back, still ends up with the thinner depth of field, which is exactly why 135mm has a reputation for the most dramatically separated, almost two-dimensional background rendering among common portrait lenses.
Where the Comparison Gets More Complicated
Maximum available aperture varies by focal length too — fast 50mm and 85mm primes commonly reach f/1.4, while fast 135mm designs more often top out around f/1.8 or f/2, since correcting a longer lens at an extremely wide aperture is a harder optical problem. In practice, the shallowest depth of field among readily available lenses often comes down to whichever specific lens offers both meaningful reach and the widest real aperture, not focal length in isolation.
Compare any two focal lengths and apertures directly for your own working distance in the DoF & Hyperfocal Calculator.
Frequently Asked Questions
Is 135mm always the better choice for maximum background blur?
Optically it usually wins on depth of field alone, but it demands considerably more working distance than 85mm or 50mm for the same framing, which isn't always practical indoors or in tight spaces — the 'best' focal length depends on the shooting environment as much as the depth-of-field math.
Does sensor size change which focal length gives the shallowest portrait depth of field?
The same relative ranking holds on any single sensor format, but the specific numbers shift — a smaller sensor needs a shorter real focal length to match a given framing, which changes the depth of field at every comparison point even though longer still beats shorter within that format.