Two thin lenses of focal lengths f1 and f2 are in contact

Two thin lenses of focal lengths f₁ and f₂ are in contact and coaxial. The power of the combination is :

The focal length of the combination	1	=	1	+	1
	f		f₁		f₂

∴ Power of the combinations, P =	f₁ + f₂		∴ P =	1
	f₁ f₂			f