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Canon FD 17mm f/4 — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published US3748021A optical prescription (11 elements in 9 groups) with a 4.3 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 | US3748021A · 11 elements in 9 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 4.3 mm (at f/4) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 43% at f/4 · -1.9 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 95° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 0.72 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 16.4 mm (-3.2%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 77 cm (50 cm – 1.27 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 FD 17mm f/4 produce?
Wide open at f/4, the Canon FD 17mm f/4 has a 4.3 mm entrance pupil (17 mm ÷ 4) and 43% bokeh roundness in the 90% corner (-1.9 EV corner falloff). In an upper-body portrait at 0.72 m, the sharp depth-of-field zone spans 77 cm (50 cm to 1.27 m) with a 95° horizontal background angle of view.
Does the Canon FD 17mm f/4 show focus breathing at portrait distance?
Based on patent US3748021A, tracing the focusing group at 0.72 m gives an effective framing focal length of 16.4 mm (-3.2% vs. the nominal 17 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Canon FD 17mm f/4?
The patent prescription (US3748021A) specifies 11 lens elements in 9 groups. The interactive Optical X-Ray above traces rays through every surface in real time.
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Compare with similar portrait lenses
- Nikon 18mm f/4 AI-s
- Leica SUPER-ELMAR-M 18mm f/3.8 ASPH
- Nikon 19mm f/4 PC-E FX
- Sony Batis 18mm F2.8
- Canon RF 16mm F2.8 STM
- Canon 14mm f/2.8 L II
Also see: depth of field, bokeh, crop factor, lens compression.