What is the best portrait lens focal length on a crop sensor?

The conversion

• APS-C (Sony, Fuji, Nikon): x1.5 — a 56mm frames like an 84mm
• Canon APS-C: x1.6 — a 50mm frames like an 80mm
• Micro Four Thirds: x2.0 — a 45mm frames like a 90mm

Depth of field converts too

Framing is not the only thing that scales. At matched framing, an f/1.4 lens on APS-C gives background blur roughly equivalent to f/2 on full frame, and f/2.8 on MFT. This is why crop-sensor portrait lenses are usually f/1.2-f/1.4 — they are chasing the same look.

Concrete picks by mount

• Fuji X: 56mm f/1.2 is the flagship portrait lens; the 50mm f/2 is the compact, weather-sealed alternative
• Sony E APS-C: Sigma 56mm f/1.4 is the standard recommendation
• Canon RF-S: the full-frame RF 85mm f/2 mounts and behaves like a 136mm, so many crop shooters use the RF 50mm f/1.8 instead
• MFT: 45mm f/1.8 class lenses are small, cheap and excellent

The budget route

A used full-frame-era 50mm f/1.8 on an adapter costs very little and frames like a short portrait lens on any crop body. Autofocus may be slower, but for static portraits it is rarely the limiting factor.

Related: Portrait lens guide - 85mm vs 50mm