Leica Summilux-SL 50mm f/1.4 ASPH. vs. Leica APO-Summicron-SL 50mm f/2 ASPH.

Ray-traced side by side from their optical patents at a 2.0 m upper-body portrait distance: compare how the Leica Summilux-SL 50mm f/1.4 ASPH. (35.7 mm entrance pupil) and Leica APO-Summicron-SL 50mm f/2 ASPH. (25.0 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	Leica Summilux-SL 50mm f/1.4 ASPH.	Leica APO-Summicron-SL 50mm f/2 ASPH.	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)	49.8 mm (-0.5%)	47.8 mm (-4.3%)	At 2.0 m, Leica Summilux-SL 50mm f/1.4 ASPH. frames like a 49.8 mm lens while Leica APO-Summicron-SL 50mm f/2 ASPH. frames like a 47.8 mm lens.
Depth of Field (Sharp Zone)	20 cm (1.92 m – 2.12 m)	29 cm (1.88 m – 2.17 m)	The Leica Summilux-SL 50mm f/1.4 ASPH. has a 30% thinner focus zone (20 cm vs. 29 cm)—requiring more precise eye focus.
Entrance Pupil Diameter	35.7 mm (f/1.4)	25.0 mm (f/2)	Distant background blur discs are 43% larger on the Leica Summilux-SL 50mm f/1.4 ASPH..
Minimum Focus Distance	0.6 m	0.35 m	Leica APO-Summicron-SL 50mm f/2 ASPH. focuses 25 cm closer (0.6 m vs. 0.35 m) for tighter close-ups.
Patent Prescription	EP3136147A1 (11/9)	US20240241349A1 (14/8)	Published optical prescriptions traced in the 3D simulator above.

Questions

Which blurs the background more, Leica Summilux-SL 50mm f/1.4 ASPH. or Leica APO-Summicron-SL 50mm f/2 ASPH.?

At the same subject framing, distant background blur scales with the entrance pupil diameter (focal length ÷ f-number). Leica Summilux-SL 50mm f/1.4 ASPH. at f/1.4 has a 35.7 mm entrance pupil, while Leica APO-Summicron-SL 50mm f/2 ASPH. at f/2 has a 25.0 mm entrance pupil.

How does working distance differ between Leica Summilux-SL 50mm f/1.4 ASPH. and Leica APO-Summicron-SL 50mm f/2 ASPH.?

For an upper-body portrait, Leica Summilux-SL 50mm f/1.4 ASPH. stands 2.01 m from the subject (sharp zone 20 cm, from 1.92 m to 2.12 m), whereas Leica APO-Summicron-SL 50mm f/2 ASPH. stands 2.01 m away (sharp zone 29 cm, from 1.88 m to 2.17 m).

How do the optical designs of Leica Summilux-SL 50mm f/1.4 ASPH. and Leica APO-Summicron-SL 50mm f/2 ASPH. compare?

Leica Summilux-SL 50mm f/1.4 ASPH. uses 11 elements in 9 groups (EP3136147A1, effective focal length 49.8 mm at portrait distance). Leica APO-Summicron-SL 50mm f/2 ASPH. uses 14 elements in 8 groups (US20240241349A1, effective focal length 47.8 mm).

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