Lensmaker's Equation formula:
1/f = (nl/nm - 1) * ( 1/r1 - 1/r2)
f: Focal Length, in meter
nl: Refractive Index of Lens Material, in meter
nm: Refractive Index of Ambient Medium, in meter
r1: Curvature Radius of the First Surface, in meter
r2: Curvature Radius of the Second Surface, in meter
This equation holds for all types of thin lenses. A radius of curvature is positive when its center of curvature lies to the right of the surface, and negative when its center of curvatures lies to the left of the surface. For Lens in close contact, the power of the combined Lens is equal to the sum of their individual Lens Powers.