Two converging lenses are to be placed in the path of parallel rays so that the rays remain parallel after passing through both lenses. How should the lenses be arranged? Explain with a neat ray diagram. (AS1)

• The rays which are parallel to the principal axis , after passing from convex lens , converges to the second focal point of the lens.

• The rays coming out from the focal point of lens, after refraction through lens, will be parallel to the principal axis.

• If the two lenses are kept parallel to each other such that the second focal point of first lens coincide with the first focal point of the second lens, then the parallel rays after refraction from first lens will converge at the second focal point.

• This focal point will act as the first focal point of second lens and the rays emerging from it, after refraction from second lens will be parallel to the principal axis.

• To conclude, both the lenses should be f1 + f2 unit apart where f1 = f2 = focal length