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Nikon 105mm f/1.8 AI-s — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published JP S59-121015A optical prescription (5 elements in 5 groups) with a 58.3 mm entrance pupil and 1 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | JP S59-121015A · 5 elements in 5 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 58.3 mm (at f/1.8) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 82% at f/1.8 (≥86% from f/2) · -0.3 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 19° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 4.21 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 108.5 mm (+3.4%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 25 cm (4.08 m – 4.34 m) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 1 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Nikon 105mm f/1.8 AI-s produce?
Wide open at f/1.8, the Nikon 105mm f/1.8 AI-s has a 58.3 mm entrance pupil (105 mm ÷ 1.8) and 82% bokeh roundness in the 90% corner (-0.3 EV corner falloff, reaching ≥86% roundness from f/2). In an upper-body portrait at 4.21 m, the sharp depth-of-field zone spans 25 cm (4.08 m to 4.34 m) with a 19° horizontal background angle of view.
Does the Nikon 105mm f/1.8 AI-s show focus breathing at portrait distance?
Based on patent JP S59-121015A, tracing the focusing group at 4.21 m gives an effective framing focal length of 108.5 mm (+3.4% vs. the nominal 105 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Nikon 105mm f/1.8 AI-s?
The patent prescription (JP S59-121015A) specifies 5 lens elements in 5 groups. The interactive Optical X-Ray above traces rays through every surface in real time.
Related comparisons
- Nikon 105mm f/1.4 FX
- Nikon AF Micro 105mm f/2.8D
- Nikon AF-S Micro 105mm f/2.8G VR
- Nikon 100mm f/2.8 Series E
- Nikon Nikkor SW 90mm f/4.5
- Nikon 85mm f/1.4 AI-s
Compare with similar portrait lenses
Also see: depth of field, bokeh, crop factor, lens compression.