What it frames
The Pentax K-3 Mark III Monochrome with the Pentax HD FA 31mm f/1.8 Limited, over a 1.75 m person in a street, with a door, a parked car and buildings. 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 sensor (23.5 x 15.6 mm) has a crop factor of 1.5, so the dashed frames are marked with the focal length that gives the same view on it.
31mm on the Pentax K-3 Mark III Monochrome frames 3.79 m × 2.52 m at 5 m: like 46mm on full frame, 42° across.
The numbers
- Frame at 5 m3.79 m × 2.52 m
- Full-frame equivalent46mm
- Angle of view42° × 28°, 49° diagonal
- Depth of field at f/1.84.26 m to 6.06 m (1.81 m)
- Depth of field at f/82.81 m to 22.5 m (19.7 m)
- Hyperfocal at f/1.828.4 m
- Hyperfocal at f/86.42 m
- Circle of confusion0.019 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.