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Nikon 18mm f/2.8D FX — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published WO2021039813A1 optical prescription (13 elements in 10 groups, 1 aspherical) with a 6.4 mm entrance pupil and 0.25 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | WO2021039813A1 · 13 elements in 10 groups (1 aspherical) | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 6.4 mm (at f/2.8) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 52% at f/2.8 · -1.6 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 92° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 0.76 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 17.3 mm (-4.1%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 47 cm (59 cm – 1.06 m) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 0.25 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Nikon 18mm f/2.8D FX produce?
Wide open at f/2.8, the Nikon 18mm f/2.8D FX has a 6.4 mm entrance pupil (18 mm ÷ 2.8) and 52% bokeh roundness in the 90% corner (-1.6 EV corner falloff). In an upper-body portrait at 0.76 m, the sharp depth-of-field zone spans 47 cm (59 cm to 1.06 m) with a 92° horizontal background angle of view.
Does the Nikon 18mm f/2.8D FX show focus breathing at portrait distance?
Based on patent WO2021039813A1, tracing the focusing group at 0.76 m gives an effective framing focal length of 17.3 mm (-4.1% vs. the nominal 18 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Nikon 18mm f/2.8D FX?
The patent prescription (WO2021039813A1) specifies 13 lens elements in 10 groups with 1 aspherical surfaces. The interactive Optical X-Ray above traces rays through every surface in real time.
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Also see: depth of field, bokeh, crop factor, lens compression.