Canon EF 50mm f/1.4 USM vs. Canon EF 50mm f/1.8 II

Ray-traced side by side from their optical patents at a 2.0 m upper-body portrait distance: compare how the Canon EF 50mm f/1.4 USM (35.7 mm entrance pupil) and Canon EF 50mm f/1.8 II (27.8 mm entrance pupil) differ in background blur size, edge bokeh, and depth of field.

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Portrait At-a-Glance Comparison (Upper Body Framing)

Optical & Portrait Metric	Canon EF 50mm f/1.4 USM	Canon EF 50mm f/1.8 II	What It Means in Practice
Upper-Body Working Distance	2.01 m	2.01 m	Identical working distance—both frame an upper-body portrait from the exact same spot.
Effective Focal Length (Breathing)	50.2 mm (+0.5%)	50.7 mm (+1.4%)	At 2.0 m, Canon EF 50mm f/1.4 USM frames like a 50.2 mm lens while Canon EF 50mm f/1.8 II frames like a 50.7 mm lens.
Depth of Field (Sharp Zone)	20 cm (1.92 m – 2.12 m)	26 cm (1.89 m – 2.15 m)	The Canon EF 50mm f/1.4 USM has a 22% thinner focus zone (20 cm vs. 26 cm)—requiring more precise eye focus.
Entrance Pupil Diameter	35.7 mm (f/1.4)	27.8 mm (f/1.8)	Distant background blur discs are 28% larger on the Canon EF 50mm f/1.4 USM.
Minimum Focus Distance	0.45 m	0.45 m	Both lenses share the same 0.45 m close-focus limit.
Patent Prescription	JP H06-242370A (7/6)	JP S62-087922A (6/5)	Published optical prescriptions traced in the 3D simulator above.

Questions

Which blurs the background more, Canon EF 50mm f/1.4 USM or Canon EF 50mm f/1.8 II?

At the same subject framing, distant background blur scales with the entrance pupil diameter (focal length ÷ f-number). Canon EF 50mm f/1.4 USM at f/1.4 has a 35.7 mm entrance pupil, while Canon EF 50mm f/1.8 II at f/1.8 has a 27.8 mm entrance pupil.

How does working distance differ between Canon EF 50mm f/1.4 USM and Canon EF 50mm f/1.8 II?

For an upper-body portrait, Canon EF 50mm f/1.4 USM stands 2.01 m from the subject (sharp zone 20 cm, from 1.92 m to 2.12 m), whereas Canon EF 50mm f/1.8 II stands 2.01 m away (sharp zone 26 cm, from 1.89 m to 2.15 m).

How do the optical designs of Canon EF 50mm f/1.4 USM and Canon EF 50mm f/1.8 II compare?

Canon EF 50mm f/1.4 USM uses 7 elements in 6 groups (JP H06-242370A, effective focal length 50.2 mm at portrait distance). Canon EF 50mm f/1.8 II uses 6 elements in 5 groups (JP S62-087922A, effective focal length 50.7 mm).

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Also see: depth of field, bokeh, crop factor, lens compression.