The power of a system of two thin lenses which share a common axis and are separated by a distance d is given by P=P₁+P₂-P₁ P₂ d . Consider two thin lenses with focal lengths f₁=30.0 cm and f₂=40.0 ~cm . There is an object in front of the first lens at a distance x f₁ . A real image is created on the screen behind the second lens. If the image on the screen is of the same size regardless of the position of the object