Why does bokeh look different between lenses at the same aperture?

The four things that change the look

Aperture blades. More blades, and rounded ones, keep highlights circular when you stop down. Straight blades produce polygons — and the same edges give point lights their star shape in the sharp areas.

Spherical aberration. Under-corrected lenses render soft, glowing background circles; over-corrected ones produce bright-rimmed rings that look busy. This is the single biggest factor in whether bokeh reads as creamy or nervous.

Aspherical elements. They fix sharpness but, when the moulding leaves fine concentric steps, they print onion-ring texture inside every highlight.

Mechanical vignetting. Toward the frame edges, the barrel clips the light cone, turning circles into cat's-eye lemon shapes. Wider apertures and shorter barrels make it worse.

What to look for in reviews

Ignore verdicts about "amazing bokeh" and look at sample images with point lights at the frame edge and in the corners. That single test exposes onion rings, cat's-eye clipping and outlining better than any chart.

Does it matter?

For headshots against a plain wall, barely. For portraits against foliage, string lights or a lit street, it dominates the image's character — which is why classic portrait primes hold their value.

Related: Portrait lens guide - f/1.2 vs f/1.8