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Nikon 13mm f/5.6 FX — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published US3728011A optical prescription (17 elements in 14 groups) with a 2.3 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 | US3728011A · 17 elements in 14 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 2.3 mm (at f/5.6) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 35% at f/5.6 · -4.1 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 110° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 0.57 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 12.6 mm (-2.7%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 271 cm (31 cm – 3.02 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 Nikon 13mm f/5.6 FX produce?
Wide open at f/5.6, the Nikon 13mm f/5.6 FX has a 2.3 mm entrance pupil (13 mm ÷ 5.6) and 35% bokeh roundness in the 90% corner (-4.1 EV corner falloff). In an upper-body portrait at 0.57 m, the sharp depth-of-field zone spans 271 cm (31 cm to 3.02 m) with a 110° horizontal background angle of view.
Does the Nikon 13mm f/5.6 FX show focus breathing at portrait distance?
Based on patent US3728011A, tracing the focusing group at 0.57 m gives an effective framing focal length of 12.6 mm (-2.7% vs. the nominal 13 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Nikon 13mm f/5.6 FX?
The patent prescription (US3728011A) specifies 17 lens elements in 14 groups. The interactive Optical X-Ray above traces rays through every surface in real time.
Related comparisons
- Nikon 15mm f/5.6
- Nikon 10.5mm f/2.8G ED DX Fisheye
- Nikon 16mm f/2.8 AI-s Fisheye
- 24mm vs 35mm focal length comparison
- 24mm vs 50mm focal length comparison
- 28mm vs 35mm focal length comparison
Compare with similar portrait lenses
- Canon 14mm f/2.8 L II
- Canon 15mm f/2.8 Fisheye
- Fujifilm XF 14mm F2.8 R
- Nikon 18mm f/4 AI-s
- Canon FD 17mm f/4
Also see: depth of field, bokeh, crop factor, lens compression.