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Nikon AF-S 20mm f/1.8G ED — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published JP2016-021011A optical prescription (16 elements in 11 groups, 3 aspherical) with a 11.1 mm entrance pupil and 0.2 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | JP2016-021011A · 16 elements in 11 groups (3 aspherical) | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 11.1 mm (at f/1.8) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 62% at f/1.8 (≥86% from f/2.8) · -1.3 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 85° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 0.84 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 19.8 mm (-1.2%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 28 cm (72 cm – 100 cm) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 0.2 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Nikon AF-S 20mm f/1.8G ED produce?
Wide open at f/1.8, the Nikon AF-S 20mm f/1.8G ED has a 11.1 mm entrance pupil (20 mm ÷ 1.8) and 62% bokeh roundness in the 90% corner (-1.3 EV corner falloff, reaching ≥86% roundness from f/2.8). In an upper-body portrait at 0.84 m, the sharp depth-of-field zone spans 28 cm (72 cm to 100 cm) with a 85° horizontal background angle of view.
Does the Nikon AF-S 20mm f/1.8G ED show focus breathing at portrait distance?
Based on patent JP2016-021011A, tracing the focusing group at 0.84 m gives an effective framing focal length of 19.8 mm (-1.2% vs. the nominal 20 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Nikon AF-S 20mm f/1.8G ED?
The patent prescription (JP2016-021011A) specifies 16 lens elements in 11 groups with 3 aspherical surfaces. The interactive Optical X-Ray above traces rays through every surface in real time.
Related comparisons
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Compare with similar portrait lenses
- Nikon NIKKOR Z 20mm f/1.8 S
- Sony FE 20mm F1.8 G
- Canon RF 20mm F1.4 L VCM
- Canon 20mm f/2.8 USM
- Nikon 24mm f/2.0 AI-s
Also see: depth of field, bokeh, crop factor, lens compression.