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Canon 28mm f/1.8 USM — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published JP S62-078520A optical prescription (5 elements in 5 groups, 1 aspherical) with a 15.6 mm entrance pupil and 0.25 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | JP S62-078520A · 5 elements in 5 groups (1 aspherical) | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 15.6 mm (at f/1.8) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 58% at f/1.8 · -1.3 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 66° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 1.15 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 27.7 mm (-1.0%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 27 cm (1.03 m – 1.30 m) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 0.25 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Canon 28mm f/1.8 USM produce?
Wide open at f/1.8, the Canon 28mm f/1.8 USM has a 15.6 mm entrance pupil (28 mm ÷ 1.8) and 58% bokeh roundness in the 90% corner (-1.3 EV corner falloff). In an upper-body portrait at 1.15 m, the sharp depth-of-field zone spans 27 cm (1.03 m to 1.30 m) with a 66° horizontal background angle of view.
Does the Canon 28mm f/1.8 USM show focus breathing at portrait distance?
Based on patent JP S62-078520A, tracing the focusing group at 1.15 m gives an effective framing focal length of 27.7 mm (-1.0% vs. the nominal 28 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Canon 28mm f/1.8 USM?
The patent prescription (JP S62-078520A) specifies 5 lens elements in 5 groups with 1 aspherical surfaces. The interactive Optical X-Ray above traces rays through every surface in real time.
Related comparisons
- Canon 24mm f/2.8 IS
- Canon 35mm f/2 IS
- Canon 35mm f/2.8 Macro
- 28mm vs 35mm focal length comparison
- 28mm vs 50mm focal length comparison
- 24mm vs 35mm focal length comparison
Compare with similar portrait lenses
- Sony FE 28mm F2
- Nikon 28mm f/2.0
- Leica Summicron-M 28mm f/2 ASPH.
- Nikon 28mm f/1.4E FX
- Nikon AF 28mm f/1.4D
- Nikon 45mm f/2.8 PC-E
Also see: depth of field, bokeh, crop factor, lens compression.