X-Ray Optics Calculator

Lens Formula

Single Lens Formula

F - Focal distance of the lens
D_s - Source distance
D_i - Image distance

             1/F = 1/D_s + 1/D_i
      or
             D_i = D_s * F /(D_s - F)

Two separated Lenses

F₁, F₂ - Focal distances of first and second lenses
D₁₂ - Distance between lenses
F - Focal distance of the two-lens system

F = (F₁F₂ + F₁D₁₂ - D₁₂²)/(F₁ + F₂ - D₁₂) (from the position of the first lens)
F = F₂ * (F₁ - D₁₂)/(F₁ + F₂ - D₁₂) (from the position of the second lens)