Lens Maker Equation Calculator

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Thin-lens ignores thickness. Use thick-lens for accurate results when the lens is not negligibly thin.
Select a material to auto-fill its refractive index, or choose "Custom" to enter your own.
Radius of the front surface (the one facing the incoming light). Positive for a convex surface, negative for concave. Use a very large number (e.g. 1e9) for a flat (plano) surface.
mm
Radius of the rear surface. Positive for a convex surface, negative for concave, using the Cartesian sign convention.
mm
Focal length (f)Converging
48.08mm

Positive = converging lens, negative = diverging lens

Optical power (P)20.8diopters (m⁻¹)
Lens typeConverging (positive) lens
Refractive index used1.52
48.08 mm
Strong diverging<-100Moderate diverging-100--20Near flat-20-0Near flat0-20Moderate converging20-100Strong converging100+

Focal length: 48.08 mm (converging lens)

  • This is a converging lens: parallel rays focus to a point 48.08 mm behind the lens.
  • The optical power is 20.800 diopters. Eyeglass prescriptions use diopters directly: a +2 D lens corrects farsightedness, a -3 D lens corrects nearsightedness.
  • Thin-lens mode assumes the lens thickness is negligible. For lenses where thickness is comparable to the radii, switch to thick-lens mode for a more accurate result.
  • The refractive index of crown glass (n = 1.520) determines how strongly the material bends light. Higher n gives shorter focal lengths for the same geometry.

Next stepTo find image distance and magnification, use the thin-lens formula: 1/f = 1/d_o + 1/d_i, where d_o is object distance and d_i is image distance.

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