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Canon RF 1200mm F8 L IS USM — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published EP4215968A1 optical prescription (25 elements in 17 groups) with a 150.0 mm entrance pupil and 4.3 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | EP4215968A1 · 25 elements in 17 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 150.0 mm (at f/8) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 87% at f/8 · -0.2 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 1° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 47.97 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 1403.0 mm (+16.9%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 112 cm (47 m – 49 m) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 4.3 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Canon RF 1200mm F8 L IS USM produce?
Wide open at f/8, the Canon RF 1200mm F8 L IS USM has a 150.0 mm entrance pupil (1200 mm ÷ 8) and 87% bokeh roundness in the 90% corner (-0.2 EV corner falloff). In an upper-body portrait at 47.97 m, the sharp depth-of-field zone spans 112 cm (47 m to 49 m) with a 1° horizontal background angle of view.
Does the Canon RF 1200mm F8 L IS USM show focus breathing at portrait distance?
Based on patent EP4215968A1, tracing the focusing group at 47.97 m gives an effective framing focal length of 1403.0 mm (+16.9% vs. the nominal 1200 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Canon RF 1200mm F8 L IS USM?
The patent prescription (EP4215968A1) specifies 25 lens elements in 17 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.