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Nikon 50mm f/1.8 AI-s — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published US4234242A optical prescription (6 elements in 5 groups) with a 27.8 mm entrance pupil and 0.45 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | US4234242A · 6 elements in 5 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 27.8 mm (at f/1.8) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 87% at f/1.8 · -0.3 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 39° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 2.01 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 51.0 mm (+2.0%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 26 cm (1.89 m – 2.15 m) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 0.45 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Nikon 50mm f/1.8 AI-s produce?
Wide open at f/1.8, the Nikon 50mm f/1.8 AI-s has a 27.8 mm entrance pupil (50 mm ÷ 1.8) and 87% bokeh roundness in the 90% corner (-0.3 EV corner falloff). In an upper-body portrait at 2.01 m, the sharp depth-of-field zone spans 26 cm (1.89 m to 2.15 m) with a 39° horizontal background angle of view.
Does the Nikon 50mm f/1.8 AI-s show focus breathing at portrait distance?
Based on patent US4234242A, tracing the focusing group at 2.01 m gives an effective framing focal length of 51.0 mm (+2.0% vs. the nominal 50 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Nikon 50mm f/1.8 AI-s?
The patent prescription (US4234242A) specifies 6 lens elements in 5 groups. The interactive Optical X-Ray above traces rays through every surface in real time.
Related comparisons
- Nikon 50mm f/1.4 AI-s
- Nikon AF-S 50mm f/1.4G
- Nikon Nikkor-S Auto 50mm f/1.4
- Nikon 50mm f/2
- Nikon 55mm f/1.2 AI
- Nikon 45mm f/2.8 PC-E
Compare with similar portrait lenses
- Nikon NIKKOR Z 50mm f/1.8 S
- Sony FE 50mm F1.8
- Canon RF 50mm F1.8 STM
- Canon EF 50mm f/1.8 II
- Nikon NIKKOR Z 35mm f/1.2 S
Also see: depth of field, bokeh, crop factor, lens compression.