Sag of a Spherical Surface calculator

Sagitta of a spherical (or conic) surface from radius and aperture.

Category: Aberrations

Formula: z = c·r²/(1 + √(1 − c²·r²)), c = 1/R

Inputs

InputParameterUnitDefault
Radius RRmm100
Half-aperture rrmm12.5

Result with the default inputs

  • Sag: 0.7843 mm

Open it with your own values: put each input in the address as a parameter, for example /calculators/sag-of-a-spherical-surface?R=100. A unit other than the listed one goes in <parameter>_unit.

Read more: Wikipedia: Sagitta (optics)

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