What it frames
The Pentax K-3 Mark III Monochrome with the Pentax smc DA* 300mm f/4 ED [IF] SDM, 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 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.
300mm on the Pentax K-3 Mark III Monochrome frames 1.18 m × 78 cm at 15 m: like 450mm on full frame, 4.5° across.
The numbers
- Frame at 15 m1.18 m × 78 cm
- Full-frame equivalent450mm
- Angle of view4.5° × 3.0°, 5.4° diagonal
- Depth of field at f/414.8 m to 15.2 m (37 cm)
- Depth of field at f/814.6 m to 15.4 m (74 cm)
- Hyperfocal at f/41197 m
- Hyperfocal at f/8599 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.