Focal Length Calculator

Your details

Choose which quantity to calculate. The other two become your inputs.
Distance from the subject to the lens. Must be positive (real object).
Distance from the lens to the sensor or film plane.
Pick your sensor to calculate angle of view and field of view. Leave as "None" for thin-lens results only.
Focal length (f)Standard / normal
49.323mm
Object distance (do)1,500mm
Image distance (di)51mm
Magnification (m)-0.034x
Optical power (1/f)20.2745D
Horizontal angle of view40.1deg
Vertical angle of view27.35deg
Diagonal angle of view47.36deg
Field of view (width)1,094.82mm
Field of view (height)729.88mm
Image typeReal, inverted, reduced
49.323 mm
Ultra-wide<24Wide24-35Normal35-70Telephoto70-135Long tele135-300Super tele300+

Focal length: 49.32 mm (Real, inverted, reduced).

  • Object distance 1,500 mm and image distance 51 mm give focal length f = (do x di) / (do + di) = 49.32 mm.
  • Magnification -0.034x: the negative sign means the image is inverted; |m| < 1 means it is smaller than the subject.
  • Optical power: 1 / 0.0493 m = 20.27 D.
  • With the selected sensor this lens captures a 40.1 deg horizontal angle of view and a field of view of 1,095 x 730 mm at the object distance.

Next stepKeep all distances in the same unit. Switch the "Solve for" dropdown to find object or image distance from a known focal length.

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