What it frames
The Pentax K-3 Mark III Monochrome with the Pentax HD D FA* 85mm f/1.4 ED SDM AW, over a 1.75 m person in front of a wall with a window. 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.
85mm on the Pentax K-3 Mark III Monochrome frames 41 cm × 28 cm at 1.5 m: like 128mm on full frame, 16° across.
The numbers
- Frame at 1.5 m41 cm × 28 cm
- Full-frame equivalent128mm
- Angle of view16° × 10°, 19° diagonal
- Depth of field at f/1.41.49 m to 1.51 m (1.5 cm)
- Depth of field at f/81.46 m to 1.55 m (8.8 cm)
- Hyperfocal at f/1.4275 m
- Hyperfocal at f/848.1 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.