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Nikon Nikkor-O 2.1cm f/4 — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published JP S43-030782B optical prescription (8 elements in 4 groups) with a 5.3 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 | JP S43-030782B · 8 elements in 4 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 5.3 mm (at f/4) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 46% at f/4 · -1.5 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 81° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 0.87 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 21.1 mm (+0.7%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 68 cm (65 cm – 1.33 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 Nikkor-O 2.1cm f/4 produce?
Wide open at f/4, the Nikon Nikkor-O 2.1cm f/4 has a 5.3 mm entrance pupil (21 mm ÷ 4) and 46% bokeh roundness in the 90% corner (-1.5 EV corner falloff). In an upper-body portrait at 0.87 m, the sharp depth-of-field zone spans 68 cm (65 cm to 1.33 m) with a 81° horizontal background angle of view.
Does the Nikon Nikkor-O 2.1cm f/4 show focus breathing at portrait distance?
Based on patent JP S43-030782B, tracing the focusing group at 0.87 m gives an effective framing focal length of 21.1 mm (+0.7% vs. the nominal 21 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Nikon Nikkor-O 2.1cm f/4?
The patent prescription (JP S43-030782B) specifies 8 lens elements in 4 groups. 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.