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Leica PA-Curtagon-R 35mm f/4 — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published US3410632A optical prescription (7 elements in 6 groups) with a 8.8 mm entrance pupil and 0.3 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | US3410632A · 7 elements in 6 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 8.8 mm (at f/4) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 79% at f/4 (≥86% from f/5.6) · -0.5 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 55° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 1.42 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 34.9 mm (-0.2%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 60 cm (1.18 m – 1.78 m) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 0.3 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Leica PA-Curtagon-R 35mm f/4 produce?
Wide open at f/4, the Leica PA-Curtagon-R 35mm f/4 has a 8.8 mm entrance pupil (35 mm ÷ 4) and 79% bokeh roundness in the 90% corner (-0.5 EV corner falloff, reaching ≥86% roundness from f/5.6). In an upper-body portrait at 1.42 m, the sharp depth-of-field zone spans 60 cm (1.18 m to 1.78 m) with a 55° horizontal background angle of view.
Does the Leica PA-Curtagon-R 35mm f/4 show focus breathing at portrait distance?
Based on patent US3410632A, tracing the focusing group at 1.42 m gives an effective framing focal length of 34.9 mm (-0.2% vs. the nominal 35 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Leica PA-Curtagon-R 35mm f/4?
The patent prescription (US3410632A) specifies 7 lens elements in 6 groups. The interactive Optical X-Ray above traces rays through every surface in real time.
Related comparisons
- 24mm vs 35mm focal length comparison
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Compare with similar portrait lenses
- Sony Sonnar FE 35mm F2.8 ZA
- Nikon 35mm f/2.8 PC
- Canon 35mm f/2.8 Macro
- Leica SUMMARON 35mm f/2.8
- Sony AF 35mm F2
- Sony FE 24mm F2.8 G
Also see: depth of field, bokeh, crop factor, lens compression.