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How close can a fixed lens focus?

Manufacturers rarely publish the minimum focus distance. It follows from focal length, aperture and sensor size.

Find the camera

SoftMay be softSharp0.7 m1.3 m0 m → 2.1 m

0.7–1.3 msharp from

Sharp from about 0.7 m. Anything nearer will be soft; between 0.7 m and 1.3 m it depends on the factory focus.

The same sensor and aperture, other lenses

  • 2.8 mm0.7–1.3 m
  • 4 mm1.3–2.7 m
  • 6 mm3.0–6.1 m
  • 8 mm5.4–11 m
  • 12 mm12–24 m

How it's calculated

  • c = sensor diagonal / 1730 = 6.43 / 1730 = 0.0037 mm
  • Hyperfocal H = f² / (N × c) = 2.8² / (1.6 × 0.0037) / 1000 = 1.32 m
  • Set at the hyperfocal distance: sharp from H / 2 = 0.7 m. Set at infinity: sharp from H = 1.3 m.
  • An estimate from published optics, not a measurement. Not for varifocal or zoom lenses, or thermal sensors.

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Questions

Why is the answer a range?
A fixed lens is focused at the factory, and that setting is not published. Set at the hyperfocal distance it is sharp from half of that distance; set at infinity it is sharp from the hyperfocal distance itself.
Does it work for varifocal lenses?
No. A varifocal or zoom lens can be focused, so its limit is in the datasheet. The calculation is for fixed lenses.
What is the circle of confusion?
The largest blur spot that still looks sharp. Here it is the sensor diagonal divided by 1730; you can type your own value.

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