What it frames
The Canon EOS 850D with the Canon EF 400mm f/5.6L USM, over a 30 cm bird on a 1 m fence post. Everything is drawn to scale: the solid frame is what the camera takes in, the dashed ones are 24, 50 and 135mm on full frame from the same spot. Its APS-C (Canon) sensor (22.3 x 14.9 mm) has a crop factor of 1.6, so the dashed frames are marked with the focal length that gives the same view on it.
400mm on the Canon EOS 850D frames 84 cm × 56 cm at 15 m: like 640mm on full frame, 3.2° across.
The numbers
- Frame at 15 m84 cm × 56 cm
- Full-frame equivalent640mm
- Angle of view3.2° × 2.1°, 3.8° diagonal
- Depth of field at f/5.614.9 m to 15.1 m (27 cm)
- Depth of field at f/814.8 m to 15.2 m (39 cm)
- Hyperfocal at f/5.61598 m
- Hyperfocal at f/81119 m
- Circle of confusion0.018 mm
How it is worked out
The frame at a distance is distance × sensor size ÷ focal length, across and up; the angle of view is 2 × atan(sensor size ÷ (2 × focal length)). Depth of field uses the thin-lens formulas: the hyperfocal distance H = f² ÷ (N × c) + f, the near limit s(H − f) ÷ (H + s − 2f) and the far limit s(H − f) ÷ (H − s), sharp to infinity from H on, with a circle of confusion c of the sensor diagonal ÷ 1500 and, on a zoom whose aperture changes, the maximum aperture taken linearly between its ends. These are for a rectilinear lens; a fisheye takes in more. Ask for this page with Accept: application/json for the numbers alone.