Find a lens for this look
eBay links may earn us a commission, at no extra cost to you.
Matching lenses from each maker's lineup, plus some classic medium and large format lenses. Email me if something is wrong or missing.
Canon RF 400mm F2.8 L IS USM — Bokeh & Optical Ray-Tracing Simulator
Interactive 3D portrait ray-traced through the published US20180095255A1 optical prescription (15 elements in 11 groups) with a 142.9 mm entrance pupil and 2.5 m minimum focus.
Optical & Portrait Specifications (Upper Body Framing)
| Optical & Portrait Metric | Measured / Patent Value | What It Means in Practice |
|---|---|---|
| Patent Prescription | US20180095255A1 · 15 elements in 11 groups | Traced surface by surface in WebGL2 |
| Entrance Pupil Diameter | 142.9 mm (at f/2.8) | Controls distant background blur disc size |
| Corner Bokeh Roundness (90% Field) | 78% at f/2.8 (≥86% from f/4) · -0.4 EV | Mechanical vignetting (cat’s-eye vs. round corner highlights) |
| Background Field of View (Compression) | 5° horizontal | Width of the background room visible behind the subject |
| Upper-Body Working Distance | 15.99 m | Camera-to-subject distance for head-to-waist framing |
| Effective Focal Length (Breathing) | 435.6 mm (+8.9%) | Actual framing focal length at portrait distance |
| Depth of Field (Sharp Zone) | 39 cm (16 m – 16 m) | Sharp zone at wide-open aperture |
| Minimum Focus Distance | 2.5 m | Closest focusing distance from the sensor |
Questions
How much background blur and corner cat's-eye does the Canon RF 400mm F2.8 L IS USM produce?
Wide open at f/2.8, the Canon RF 400mm F2.8 L IS USM has a 142.9 mm entrance pupil (400 mm ÷ 2.8) and 78% bokeh roundness in the 90% corner (-0.4 EV corner falloff, reaching ≥86% roundness from f/4). In an upper-body portrait at 15.99 m, the sharp depth-of-field zone spans 39 cm (16 m to 16 m) with a 5° horizontal background angle of view.
Does the Canon RF 400mm F2.8 L IS USM show focus breathing at portrait distance?
Based on patent US20180095255A1, tracing the focusing group at 15.99 m gives an effective framing focal length of 435.6 mm (+8.9% vs. the nominal 400 mm). You can toggle "Match subject size" in the simulator to see the framing shift live.
What optical design is inside the Canon RF 400mm F2.8 L IS USM?
The patent prescription (US20180095255A1) specifies 15 lens elements in 11 groups. The interactive Optical X-Ray above traces rays through every surface in real time.
Related comparisons
- 50mm vs 200mm focal length comparison
- 70mm vs 200mm focal length comparison
- 85mm vs 200mm focal length comparison
- 105mm vs 200mm focal length comparison
- 135mm vs 200mm focal length comparison
- 35mm vs 135mm focal length comparison
Compare with similar portrait lenses
- Canon 400mm f/2.8 L IS
- Nikon NIKKOR Z 400mm f/2.8 TC VR S
- Canon 400mm f/5.6 L
- Leica Telyt 400mm f/5
- Nikon 300mm f/2 ED IF
- Sony FE 600mm F4 GM OSS
Also see: depth of field, bokeh, crop factor, lens compression.