Shack Hartmann Equation Formula

Equation for calculate shack hartmann equation is,

$\frac{1}{f}=\frac{1}{f+Z-Z_0}+\frac{1}{R+L}$

where,
Z = source position,
Z₀ = source position for a collimated beam,
L = distance between the wavefront sensor and the principal plane of the lens,
R = Radius of curvature of the wavefront coming out of the test lens, and
f = The focal length