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Nikon 55mm f/1.2 AI — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published US3738736A optical prescription (7 elements in 6 groups) with a 45.8 mm entrance pupil and 0.5 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | US3738736A · 7 elements in 6 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 45.8 mm (at f/1.2) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 71% at f/1.2 (≥86% from f/1.8) · -0.7 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 36° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 2.21 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 54.9 mm (-0.2%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 17 cm (2.13 m – 2.30 m) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 0.5 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Nikon 55mm f/1.2 AI produce?
Wide open at f/1.2, the Nikon 55mm f/1.2 AI has a 45.8 mm entrance pupil (55 mm ÷ 1.2) and 71% bokeh roundness in the 90% corner (-0.7 EV corner falloff, reaching ≥86% roundness from f/1.8). In an upper-body portrait at 2.21 m, the sharp depth-of-field zone spans 17 cm (2.13 m to 2.30 m) with a 36° horizontal background angle of view.
Does the Nikon 55mm f/1.2 AI show focus breathing at portrait distance?
Based on patent US3738736A, tracing the focusing group at 2.21 m gives an effective framing focal length of 54.9 mm (-0.2% vs. the nominal 55 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Nikon 55mm f/1.2 AI?
The patent prescription (US3738736A) specifies 7 lens elements in 6 groups. The interactive Optical X-Ray above traces rays through every surface in real time.
Related comparisons
- Nikon 55mm f/2.8 Micro AI-s
- Nikon 58mm f/1.2 Noct-NIKKOR
- Nikon 58mm f/1.4 G FX
- Nikon Nikkor-S Auto 58mm f/1.4
- Nikon 50mm f/1.4 AI-s
- Nikon AF-S 50mm f/1.4G
Compare with similar portrait lenses
Also see: depth of field, bokeh, crop factor, lens compression.