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Nikon NIKKOR 180mm f/2.8 AI — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published US4338001A optical prescription (5 elements in 5 groups) with a 64.3 mm entrance pupil and 1.8 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | US4338001A · 5 elements in 5 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 64.3 mm (at f/2.8) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 77% at f/2.8 (≥86% from f/4) · -0.4 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 11° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 7.20 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 191.8 mm (+6.5%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 39 cm (7.01 m – 7.40 m) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 1.8 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Nikon NIKKOR 180mm f/2.8 AI produce?
Wide open at f/2.8, the Nikon NIKKOR 180mm f/2.8 AI has a 64.3 mm entrance pupil (180 mm ÷ 2.8) and 77% bokeh roundness in the 90% corner (-0.4 EV corner falloff, reaching ≥86% roundness from f/4). In an upper-body portrait at 7.20 m, the sharp depth-of-field zone spans 39 cm (7.01 m to 7.40 m) with a 11° horizontal background angle of view.
Does the Nikon NIKKOR 180mm f/2.8 AI show focus breathing at portrait distance?
Based on patent US4338001A, tracing the focusing group at 7.20 m gives an effective framing focal length of 191.8 mm (+6.5% vs. the nominal 180 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Nikon NIKKOR 180mm f/2.8 AI?
The patent prescription (US4338001A) specifies 5 lens elements in 5 groups. The interactive Optical X-Ray above traces rays through every surface in real time.
Related comparisons
- Nikon 200mm f/2 VR II FX
- Nikon 200mm f/4 Micro-NIKKOR
- Nikon AF DC 135mm f/2D
- Nikon NIKKOR 135mm f/2 AI-s
- Nikon 135mm f/2.8 AI-s
- Nikon 135mm f/2.8 Series E
Compare with similar portrait lenses
Also see: depth of field, bokeh, crop factor, lens compression.