Sony FE 85mm f/1.8 vs. Sony FE 135mm F1.8 GM

Ray-traced side by side from their optical patents for the same upper-body portrait framing: compare the Sony FE 85mm f/1.8 (3.4 m working distance, 47.2 mm pupil) against the Sony FE 135mm F1.8 GM (5.4 m working distance, 75.0 mm pupil).

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

Optical & Portrait Metric Sony FE 85mm f/1.8 Sony FE 135mm F1.8 GM What It Means in Practice
Upper-Body Working Distance 3.41 m 5.40 m The Sony FE 135mm F1.8 GM requires 2.0 m more room behind you for the same subject size.
Effective Focal Length (Breathing) 89.9 mm (+5.8%) 130.8 mm (-3.1%) Sony FE 85mm f/1.8 frames like 89.9 mm (+5.8%) at 3.4 m; Sony FE 135mm F1.8 GM frames like 130.8 mm (-3.1%) at 5.4 m.
Depth of Field (Sharp Zone) 25 cm (3.29 m – 3.54 m) 25 cm (5.28 m – 5.53 m) Both lenses deliver the exact same 25 cm sharp focus zone.
Entrance Pupil Diameter 47.2 mm (f/1.8) 75.0 mm (f/1.8) Distant background blur discs are 59% larger on the Sony FE 135mm F1.8 GM.
Minimum Focus Distance 0.8 m 0.7 m Sony FE 135mm F1.8 GM focuses 10 cm closer (0.8 m vs. 0.7 m) for tighter close-ups.
Patent Prescription JP2015-096915A (11/8) WO2019187633A1 (13/10) Published optical prescriptions traced in the 3D simulator above.

Questions

Which blurs the background more, Sony FE 85mm f/1.8 or Sony FE 135mm F1.8 GM?

At the same subject framing, distant background blur scales with the entrance pupil diameter (focal length ÷ f-number). Sony FE 85mm f/1.8 at f/1.8 has a 47.2 mm entrance pupil, while Sony FE 135mm F1.8 GM at f/1.8 has a 75.0 mm entrance pupil.

How does working distance differ between Sony FE 85mm f/1.8 and Sony FE 135mm F1.8 GM?

For an upper-body portrait, Sony FE 85mm f/1.8 stands 3.41 m from the subject (sharp zone 25 cm, from 3.29 m to 3.54 m), whereas Sony FE 135mm F1.8 GM stands 5.40 m away (sharp zone 25 cm, from 5.28 m to 5.53 m).

How do the optical designs of Sony FE 85mm f/1.8 and Sony FE 135mm F1.8 GM compare?

Sony FE 85mm f/1.8 uses 11 elements in 8 groups (JP2015-096915A, effective focal length 89.9 mm at portrait distance). Sony FE 135mm F1.8 GM uses 13 elements in 10 groups (WO2019187633A1, effective focal length 130.8 mm).

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