Front Focal Length Formula

Equation for calculate front focal length is,

$F F F = \frac{f_{1} (f_{2} - d)}{(f_{1} + f_{2}) - d}$

where,

f₁ = Focal length of one of the lenses (m)

f₂ = Focal length of the other one of the lenses (m)

d = Distance between the lenses (m)

FFL = front focal length (m)