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Canon RF-S 3.9mm F3.5 STM DUAL FISHEYE — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published US20240241345A1 optical prescription (11 elements in 8 groups) with a 1.1 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 | US20240241345A1 · 11 elements in 8 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 1.1 mm (at f/3.5) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 100% at f/3.5 · -0.4 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 143° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 0.31 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 3.9 mm (-0.0%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | infinity (10 cm – infinity) | 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 Canon RF-S 3.9mm F3.5 STM DUAL FISHEYE produce?
Wide open at f/3.5, the Canon RF-S 3.9mm F3.5 STM DUAL FISHEYE has a 1.1 mm entrance pupil (3.9 mm ÷ 3.5) and 100% bokeh roundness in the 90% corner (-0.4 EV corner falloff). In an upper-body portrait at 0.31 m, the sharp depth-of-field zone spans infinity (10 cm to infinity) with a 143° horizontal background angle of view.
Does the Canon RF-S 3.9mm F3.5 STM DUAL FISHEYE show focus breathing at portrait distance?
Based on patent US20240241345A1, tracing the focusing group at 0.31 m gives an effective framing focal length of 3.9 mm (-0.0% vs. the nominal 3.9 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Canon RF-S 3.9mm F3.5 STM DUAL FISHEYE?
The patent prescription (US20240241345A1) specifies 11 lens elements in 8 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.