Question

Two converging lenses of unequal focal lengths can be used to reduce the aperture of a parallel beam of light without loosing the energy of the light. This increase the intensity. Describe how the converging lenses should be placed to do this.

Answer 1

Let the two converging lenses be L₁ and L₂, with focal lengths f₁ and f₂ respectively.
To reduce the aperture of a parallel beam of light without losing the energy of the light and also increase the intensity, we have to place the lens L₂ within the focal range of L_1.