Sony FE 50mm F1.2 GM vs Sony Sonnar FE 55mm F1.8 ZA — Optical Ray-Tracing & Bokeh Comparison

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

Optical & Portrait Metric	Sony FE 50mm F1.2 GM	Sony Sonnar FE 55mm F1.8 ZA	What It Means in Practice
Upper-Body Working Distance	2.01 m	2.21 m	The Sony Sonnar FE 55mm F1.8 ZA requires 0.2 m more room behind you for the same subject size.
Effective Focal Length (Breathing)	50.7 mm (+1.5%)	54.2 mm (-1.5%)	Sony FE 50mm F1.2 GM frames like 50.7 mm (+1.5%) at 2.0 m; Sony Sonnar FE 55mm F1.8 ZA frames like 54.2 mm (-1.5%) at 2.2 m.
Depth of Field (Sharp Zone)	17 cm (1.93 m – 2.10 m)	26 cm (2.09 m – 2.35 m)	The Sony FE 50mm F1.2 GM has a 33% thinner focus zone (17 cm vs. 26 cm)—requiring more precise eye focus.
Entrance Pupil Diameter	41.7 mm (f/1.2)	30.6 mm (f/1.8)	Distant background blur discs are 36% larger on the Sony FE 50mm F1.2 GM.
Minimum Focus Distance	0.4 m	0.5 m	Sony FE 50mm F1.2 GM focuses 10 cm closer (0.4 m vs. 0.5 m) for tighter close-ups.
Patent Prescription	WO2017138250A1 (12/9)	US20150092100A1 (7/5)	Published optical prescriptions traced in the 3D simulator above.

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Questions

Which blurs the background more, Sony FE 50mm F1.2 GM or Sony Sonnar FE 55mm F1.8 ZA?

At the same subject framing, distant background blur scales with the entrance pupil diameter (focal length ÷ f-number). Sony FE 50mm F1.2 GM at f/1.2 has a 41.7 mm entrance pupil, while Sony Sonnar FE 55mm F1.8 ZA at f/1.8 has a 30.6 mm entrance pupil.

How does working distance differ between Sony FE 50mm F1.2 GM and Sony Sonnar FE 55mm F1.8 ZA?

For an upper-body portrait, Sony FE 50mm F1.2 GM stands 2.01 m from the subject (sharp zone 17 cm, from 1.93 m to 2.10 m), whereas Sony Sonnar FE 55mm F1.8 ZA stands 2.21 m away (sharp zone 26 cm, from 2.09 m to 2.35 m).

How do the optical designs of Sony FE 50mm F1.2 GM and Sony Sonnar FE 55mm F1.8 ZA compare?

Sony FE 50mm F1.2 GM uses 12 elements in 9 groups (WO2017138250A1, effective focal length 50.7 mm at portrait distance). Sony Sonnar FE 55mm F1.8 ZA uses 7 elements in 5 groups (US20150092100A1, effective focal length 54.2 mm).

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